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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>What’s New in Python 2.6 — Python 3.6.7 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="What’s New in Python 2.5" href="2.5.html" /> <link rel="prev" title="What’s New in Python 2.7" href="2.7.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/whatsnew/2.6.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="2.5.html" title="What’s New in Python 2.5" accesskey="N">next</a> |</li> <li class="right" > <a href="2.7.html" title="What’s New in Python 2.7" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.6.7 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">What’s New in Python</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="what-s-new-in-python-2-6"> <span id="whats-new-in-2-6"></span><h1>What’s New in Python 2.6<a class="headerlink" href="#what-s-new-in-python-2-6" title="Permalink to this headline">¶</a></h1> <table class="docutils field-list" frame="void" rules="none"> <col class="field-name" /> <col class="field-body" /> <tbody valign="top"> <tr class="field-odd field"><th class="field-name">Author:</th><td class="field-body">A.M. Kuchling (amk at amk.ca)</td> </tr> </tbody> </table> <p>This article explains the new features in Python 2.6, released on October 1 2008. The release schedule is described in <span class="target" id="index-0"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0361"><strong>PEP 361</strong></a>.</p> <p>The major theme of Python 2.6 is preparing the migration path to Python 3.0, a major redesign of the language. Whenever possible, Python 2.6 incorporates new features and syntax from 3.0 while remaining compatible with existing code by not removing older features or syntax. When it’s not possible to do that, Python 2.6 tries to do what it can, adding compatibility functions in a <code class="xref py py-mod docutils literal notranslate"><span class="pre">future_builtins</span></code> module and a <code class="xref std std-option docutils literal notranslate"><span class="pre">-3</span></code> switch to warn about usages that will become unsupported in 3.0.</p> <p>Some significant new packages have been added to the standard library, such as the <a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> and <a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> modules, but there aren’t many new features that aren’t related to Python 3.0 in some way.</p> <p>Python 2.6 also sees a number of improvements and bugfixes throughout the source. A search through the change logs finds there were 259 patches applied and 612 bugs fixed between Python 2.5 and 2.6. Both figures are likely to be underestimates.</p> <p>This article doesn’t attempt to provide a complete specification of the new features, but instead provides a convenient overview. For full details, you should refer to the documentation for Python 2.6. If you want to understand the rationale for the design and implementation, refer to the PEP for a particular new feature. Whenever possible, “What’s New in Python” links to the bug/patch item for each change.</p> <div class="section" id="python-3-0"> <h2>Python 3.0<a class="headerlink" href="#python-3-0" title="Permalink to this headline">¶</a></h2> <p>The development cycle for Python versions 2.6 and 3.0 was synchronized, with the alpha and beta releases for both versions being made on the same days. The development of 3.0 has influenced many features in 2.6.</p> <p>Python 3.0 is a far-ranging redesign of Python that breaks compatibility with the 2.x series. This means that existing Python code will need some conversion in order to run on Python 3.0. However, not all the changes in 3.0 necessarily break compatibility. In cases where new features won’t cause existing code to break, they’ve been backported to 2.6 and are described in this document in the appropriate place. Some of the 3.0-derived features are:</p> <ul class="simple"> <li>A <a class="reference internal" href="../reference/datamodel.html#object.__complex__" title="object.__complex__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__complex__()</span></code></a> method for converting objects to a complex number.</li> <li>Alternate syntax for catching exceptions: <code class="docutils literal notranslate"><span class="pre">except</span> <span class="pre">TypeError</span> <span class="pre">as</span> <span class="pre">exc</span></code>.</li> <li>The addition of <a class="reference internal" href="../library/functools.html#functools.reduce" title="functools.reduce"><code class="xref py py-func docutils literal notranslate"><span class="pre">functools.reduce()</span></code></a> as a synonym for the built-in <code class="xref py py-func docutils literal notranslate"><span class="pre">reduce()</span></code> function.</li> </ul> <p>Python 3.0 adds several new built-in functions and changes the semantics of some existing builtins. Functions that are new in 3.0 such as <a class="reference internal" href="../library/functions.html#bin" title="bin"><code class="xref py py-func docutils literal notranslate"><span class="pre">bin()</span></code></a> have simply been added to Python 2.6, but existing builtins haven’t been changed; instead, the <code class="xref py py-mod docutils literal notranslate"><span class="pre">future_builtins</span></code> module has versions with the new 3.0 semantics. Code written to be compatible with 3.0 can do <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">future_builtins</span> <span class="pre">import</span> <span class="pre">hex,</span> <span class="pre">map</span></code> as necessary.</p> <p>A new command-line switch, <code class="xref std std-option docutils literal notranslate"><span class="pre">-3</span></code>, enables warnings about features that will be removed in Python 3.0. You can run code with this switch to see how much work will be necessary to port code to 3.0. The value of this switch is available to Python code as the boolean variable <code class="xref py py-data docutils literal notranslate"><span class="pre">sys.py3kwarning</span></code>, and to C extension code as <code class="xref c c-data docutils literal notranslate"><span class="pre">Py_Py3kWarningFlag</span></code>.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <p class="last">The 3xxx series of PEPs, which contains proposals for Python 3.0. <span class="target" id="index-1"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3000"><strong>PEP 3000</strong></a> describes the development process for Python 3.0. Start with <span class="target" id="index-2"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3100"><strong>PEP 3100</strong></a> that describes the general goals for Python 3.0, and then explore the higher-numbered PEPS that propose specific features.</p> </div> </div> <div class="section" id="changes-to-the-development-process"> <h2>Changes to the Development Process<a class="headerlink" href="#changes-to-the-development-process" title="Permalink to this headline">¶</a></h2> <p>While 2.6 was being developed, the Python development process underwent two significant changes: we switched from SourceForge’s issue tracker to a customized Roundup installation, and the documentation was converted from LaTeX to reStructuredText.</p> <div class="section" id="new-issue-tracker-roundup"> <h3>New Issue Tracker: Roundup<a class="headerlink" href="#new-issue-tracker-roundup" title="Permalink to this headline">¶</a></h3> <p>For a long time, the Python developers had been growing increasingly annoyed by SourceForge’s bug tracker. SourceForge’s hosted solution doesn’t permit much customization; for example, it wasn’t possible to customize the life cycle of issues.</p> <p>The infrastructure committee of the Python Software Foundation therefore posted a call for issue trackers, asking volunteers to set up different products and import some of the bugs and patches from SourceForge. Four different trackers were examined: <a class="reference external" href="https://www.atlassian.com/software/jira/">Jira</a>, <a class="reference external" href="https://launchpad.net/">Launchpad</a>, <a class="reference external" href="http://roundup.sourceforge.net/">Roundup</a>, and <a class="reference external" href="https://trac.edgewall.org/">Trac</a>. The committee eventually settled on Jira and Roundup as the two candidates. Jira is a commercial product that offers no-cost hosted instances to free-software projects; Roundup is an open-source project that requires volunteers to administer it and a server to host it.</p> <p>After posting a call for volunteers, a new Roundup installation was set up at <a class="reference external" href="https://bugs.python.org">https://bugs.python.org</a>. One installation of Roundup can host multiple trackers, and this server now also hosts issue trackers for Jython and for the Python web site. It will surely find other uses in the future. Where possible, this edition of “What’s New in Python” links to the bug/patch item for each change.</p> <p>Hosting of the Python bug tracker is kindly provided by <a class="reference external" href="http://www.upfrontsystems.co.za/">Upfront Systems</a> of Stellenbosch, South Africa. Martin von Löwis put a lot of effort into importing existing bugs and patches from SourceForge; his scripts for this import operation are at <a class="reference external" href="http://svn.python.org/view/tracker/importer/">http://svn.python.org/view/tracker/importer/</a> and may be useful to other projects wishing to move from SourceForge to Roundup.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><a class="reference external" href="https://bugs.python.org">https://bugs.python.org</a></dt> <dd>The Python bug tracker.</dd> <dt><a class="reference external" href="http://bugs.jython.org">http://bugs.jython.org</a>:</dt> <dd>The Jython bug tracker.</dd> <dt><a class="reference external" href="http://roundup.sourceforge.net/">http://roundup.sourceforge.net/</a></dt> <dd>Roundup downloads and documentation.</dd> <dt><a class="reference external" href="http://svn.python.org/view/tracker/importer/">http://svn.python.org/view/tracker/importer/</a></dt> <dd>Martin von Löwis’s conversion scripts.</dd> </dl> </div> </div> <div class="section" id="new-documentation-format-restructuredtext-using-sphinx"> <h3>New Documentation Format: reStructuredText Using Sphinx<a class="headerlink" href="#new-documentation-format-restructuredtext-using-sphinx" title="Permalink to this headline">¶</a></h3> <p>The Python documentation was written using LaTeX since the project started around 1989. In the 1980s and early 1990s, most documentation was printed out for later study, not viewed online. LaTeX was widely used because it provided attractive printed output while remaining straightforward to write once the basic rules of the markup were learned.</p> <p>Today LaTeX is still used for writing publications destined for printing, but the landscape for programming tools has shifted. We no longer print out reams of documentation; instead, we browse through it online and HTML has become the most important format to support. Unfortunately, converting LaTeX to HTML is fairly complicated and Fred L. Drake Jr., the long-time Python documentation editor, spent a lot of time maintaining the conversion process. Occasionally people would suggest converting the documentation into SGML and later XML, but performing a good conversion is a major task and no one ever committed the time required to finish the job.</p> <p>During the 2.6 development cycle, Georg Brandl put a lot of effort into building a new toolchain for processing the documentation. The resulting package is called Sphinx, and is available from <a class="reference external" href="http://sphinx-doc.org/">http://sphinx-doc.org/</a>.</p> <p>Sphinx concentrates on HTML output, producing attractively styled and modern HTML; printed output is still supported through conversion to LaTeX. The input format is reStructuredText, a markup syntax supporting custom extensions and directives that is commonly used in the Python community.</p> <p>Sphinx is a standalone package that can be used for writing, and almost two dozen other projects (<a class="reference external" href="http://sphinx-doc.org/examples.html">listed on the Sphinx web site</a>) have adopted Sphinx as their documentation tool.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><a class="reference external" href="https://devguide.python.org/documenting/">Documenting Python</a></dt> <dd>Describes how to write for Python’s documentation.</dd> <dt><a class="reference external" href="http://sphinx-doc.org/">Sphinx</a></dt> <dd>Documentation and code for the Sphinx toolchain.</dd> <dt><a class="reference external" href="http://docutils.sourceforge.net">Docutils</a></dt> <dd>The underlying reStructuredText parser and toolset.</dd> </dl> </div> </div> </div> <div class="section" id="pep-343-the-with-statement"> <span id="pep-0343"></span><h2>PEP 343: The ‘with’ statement<a class="headerlink" href="#pep-343-the-with-statement" title="Permalink to this headline">¶</a></h2> <p>The previous version, Python 2.5, added the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement as an optional feature, to be enabled by a <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">__future__</span> <span class="pre">import</span> <span class="pre">with_statement</span></code> directive. In 2.6 the statement no longer needs to be specially enabled; this means that <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> is now always a keyword. The rest of this section is a copy of the corresponding section from the “What’s New in Python 2.5” document; if you’re familiar with the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement from Python 2.5, you can skip this section.</p> <p>The ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement clarifies code that previously would use <code class="docutils literal notranslate"><span class="pre">try...finally</span></code> blocks to ensure that clean-up code is executed. In this section, I’ll discuss the statement as it will commonly be used. In the next section, I’ll examine the implementation details and show how to write objects for use with this statement.</p> <p>The ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement is a control-flow structure whose basic structure is:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">expression</span> <span class="p">[</span><span class="k">as</span> <span class="n">variable</span><span class="p">]:</span> <span class="k">with</span><span class="o">-</span><span class="n">block</span> </pre></div> </div> <p>The expression is evaluated, and it should result in an object that supports the context management protocol (that is, has <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__enter__()</span></code></a> and <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> methods).</p> <p>The object’s <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__enter__()</span></code></a> is called before <em>with-block</em> is executed and therefore can run set-up code. It also may return a value that is bound to the name <em>variable</em>, if given. (Note carefully that <em>variable</em> is <em>not</em> assigned the result of <em>expression</em>.)</p> <p>After execution of the <em>with-block</em> is finished, the object’s <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> method is called, even if the block raised an exception, and can therefore run clean-up code.</p> <p>Some standard Python objects now support the context management protocol and can be used with the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement. File objects are one example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'/etc/passwd'</span><span class="p">,</span> <span class="s1">'r'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span> <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">f</span><span class="p">:</span> <span class="nb">print</span> <span class="n">line</span> <span class="o">...</span> <span class="n">more</span> <span class="n">processing</span> <span class="n">code</span> <span class="o">...</span> </pre></div> </div> <p>After this statement has executed, the file object in <em>f</em> will have been automatically closed, even if the <a class="reference internal" href="../reference/compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code></a> loop raised an exception part-way through the block.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">In this case, <em>f</em> is the same object created by <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a>, because <code class="xref py py-meth docutils literal notranslate"><span class="pre">file.__enter__()</span></code> returns <em>self</em>.</p> </div> <p>The <a class="reference internal" href="../library/threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> module’s locks and condition variables also support the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">lock</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Lock</span><span class="p">()</span> <span class="k">with</span> <span class="n">lock</span><span class="p">:</span> <span class="c1"># Critical section of code</span> <span class="o">...</span> </pre></div> </div> <p>The lock is acquired before the block is executed and always released once the block is complete.</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">localcontext()</span></code> function in the <a class="reference internal" href="../library/decimal.html#module-decimal" title="decimal: Implementation of the General Decimal Arithmetic Specification."><code class="xref py py-mod docutils literal notranslate"><span class="pre">decimal</span></code></a> module makes it easy to save and restore the current decimal context, which encapsulates the desired precision and rounding characteristics for computations:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">decimal</span> <span class="k">import</span> <span class="n">Decimal</span><span class="p">,</span> <span class="n">Context</span><span class="p">,</span> <span class="n">localcontext</span> <span class="c1"># Displays with default precision of 28 digits</span> <span class="n">v</span> <span class="o">=</span> <span class="n">Decimal</span><span class="p">(</span><span class="s1">'578'</span><span class="p">)</span> <span class="nb">print</span> <span class="n">v</span><span class="o">.</span><span class="n">sqrt</span><span class="p">()</span> <span class="k">with</span> <span class="n">localcontext</span><span class="p">(</span><span class="n">Context</span><span class="p">(</span><span class="n">prec</span><span class="o">=</span><span class="mi">16</span><span class="p">)):</span> <span class="c1"># All code in this block uses a precision of 16 digits.</span> <span class="c1"># The original context is restored on exiting the block.</span> <span class="nb">print</span> <span class="n">v</span><span class="o">.</span><span class="n">sqrt</span><span class="p">()</span> </pre></div> </div> <div class="section" id="writing-context-managers"> <span id="new-26-context-managers"></span><h3>Writing Context Managers<a class="headerlink" href="#writing-context-managers" title="Permalink to this headline">¶</a></h3> <p>Under the hood, the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement is fairly complicated. Most people will only use ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ in company with existing objects and don’t need to know these details, so you can skip the rest of this section if you like. Authors of new objects will need to understand the details of the underlying implementation and should keep reading.</p> <p>A high-level explanation of the context management protocol is:</p> <ul class="simple"> <li>The expression is evaluated and should result in an object called a “context manager”. The context manager must have <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__enter__()</span></code></a> and <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> methods.</li> <li>The context manager’s <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__enter__()</span></code></a> method is called. The value returned is assigned to <em>VAR</em>. If no <code class="docutils literal notranslate"><span class="pre">as</span> <span class="pre">VAR</span></code> clause is present, the value is simply discarded.</li> <li>The code in <em>BLOCK</em> is executed.</li> <li>If <em>BLOCK</em> raises an exception, the context manager’s <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> method is called with three arguments, the exception details (<code class="docutils literal notranslate"><span class="pre">type,</span> <span class="pre">value,</span> <span class="pre">traceback</span></code>, the same values returned by <a class="reference internal" href="../library/sys.html#sys.exc_info" title="sys.exc_info"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exc_info()</span></code></a>, which can also be <code class="docutils literal notranslate"><span class="pre">None</span></code> if no exception occurred). The method’s return value controls whether an exception is re-raised: any false value re-raises the exception, and <code class="docutils literal notranslate"><span class="pre">True</span></code> will result in suppressing it. You’ll only rarely want to suppress the exception, because if you do the author of the code containing the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement will never realize anything went wrong.</li> <li>If <em>BLOCK</em> didn’t raise an exception, the <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> method is still called, but <em>type</em>, <em>value</em>, and <em>traceback</em> are all <code class="docutils literal notranslate"><span class="pre">None</span></code>.</li> </ul> <p>Let’s think through an example. I won’t present detailed code but will only sketch the methods necessary for a database that supports transactions.</p> <p>(For people unfamiliar with database terminology: a set of changes to the database are grouped into a transaction. Transactions can be either committed, meaning that all the changes are written into the database, or rolled back, meaning that the changes are all discarded and the database is unchanged. See any database textbook for more information.)</p> <p>Let’s assume there’s an object representing a database connection. Our goal will be to let the user write code like this:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">db_connection</span> <span class="o">=</span> <span class="n">DatabaseConnection</span><span class="p">()</span> <span class="k">with</span> <span class="n">db_connection</span> <span class="k">as</span> <span class="n">cursor</span><span class="p">:</span> <span class="n">cursor</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="s1">'insert into ...'</span><span class="p">)</span> <span class="n">cursor</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="s1">'delete from ...'</span><span class="p">)</span> <span class="c1"># ... more operations ...</span> </pre></div> </div> <p>The transaction should be committed if the code in the block runs flawlessly or rolled back if there’s an exception. Here’s the basic interface for <code class="xref py py-class docutils literal notranslate"><span class="pre">DatabaseConnection</span></code> that I’ll assume:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">DatabaseConnection</span><span class="p">:</span> <span class="c1"># Database interface</span> <span class="k">def</span> <span class="nf">cursor</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="s2">"Returns a cursor object and starts a new transaction"</span> <span class="k">def</span> <span class="nf">commit</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="s2">"Commits current transaction"</span> <span class="k">def</span> <span class="nf">rollback</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="s2">"Rolls back current transaction"</span> </pre></div> </div> <p>The <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__enter__()</span></code></a> method is pretty easy, having only to start a new transaction. For this application the resulting cursor object would be a useful result, so the method will return it. The user can then add <code class="docutils literal notranslate"><span class="pre">as</span> <span class="pre">cursor</span></code> to their ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement to bind the cursor to a variable name.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">DatabaseConnection</span><span class="p">:</span> <span class="o">...</span> <span class="k">def</span> <span class="nf">__enter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="c1"># Code to start a new transaction</span> <span class="n">cursor</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">cursor</span><span class="p">()</span> <span class="k">return</span> <span class="n">cursor</span> </pre></div> </div> <p>The <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> method is the most complicated because it’s where most of the work has to be done. The method has to check if an exception occurred. If there was no exception, the transaction is committed. The transaction is rolled back if there was an exception.</p> <p>In the code below, execution will just fall off the end of the function, returning the default value of <code class="docutils literal notranslate"><span class="pre">None</span></code>. <code class="docutils literal notranslate"><span class="pre">None</span></code> is false, so the exception will be re-raised automatically. If you wished, you could be more explicit and add a <a class="reference internal" href="../reference/simple_stmts.html#return"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">return</span></code></a> statement at the marked location.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">DatabaseConnection</span><span class="p">:</span> <span class="o">...</span> <span class="k">def</span> <span class="nf">__exit__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">type</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">tb</span><span class="p">):</span> <span class="k">if</span> <span class="n">tb</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span> <span class="c1"># No exception, so commit</span> <span class="bp">self</span><span class="o">.</span><span class="n">commit</span><span class="p">()</span> <span class="k">else</span><span class="p">:</span> <span class="c1"># Exception occurred, so rollback.</span> <span class="bp">self</span><span class="o">.</span><span class="n">rollback</span><span class="p">()</span> <span class="c1"># return False</span> </pre></div> </div> </div> <div class="section" id="the-contextlib-module"> <span id="new-module-contextlib"></span><h3>The contextlib module<a class="headerlink" href="#the-contextlib-module" title="Permalink to this headline">¶</a></h3> <p>The <a class="reference internal" href="../library/contextlib.html#module-contextlib" title="contextlib: Utilities for with-statement contexts."><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextlib</span></code></a> module provides some functions and a decorator that are useful when writing objects for use with the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement.</p> <p>The decorator is called <code class="xref py py-func docutils literal notranslate"><span class="pre">contextmanager()</span></code>, and lets you write a single generator function instead of defining a new class. The generator should yield exactly one value. The code up to the <a class="reference internal" href="../reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">yield</span></code></a> will be executed as the <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__enter__()</span></code></a> method, and the value yielded will be the method’s return value that will get bound to the variable in the ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement’s <a class="reference internal" href="../reference/compound_stmts.html#as"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">as</span></code></a> clause, if any. The code after the <a class="reference internal" href="../reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">yield</span></code></a> will be executed in the <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> method. Any exception raised in the block will be raised by the <a class="reference internal" href="../reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">yield</span></code></a> statement.</p> <p>Using this decorator, our database example from the previous section could be written as:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">contextlib</span> <span class="k">import</span> <span class="n">contextmanager</span> <span class="nd">@contextmanager</span> <span class="k">def</span> <span class="nf">db_transaction</span><span class="p">(</span><span class="n">connection</span><span class="p">):</span> <span class="n">cursor</span> <span class="o">=</span> <span class="n">connection</span><span class="o">.</span><span class="n">cursor</span><span class="p">()</span> <span class="k">try</span><span class="p">:</span> <span class="k">yield</span> <span class="n">cursor</span> <span class="k">except</span><span class="p">:</span> <span class="n">connection</span><span class="o">.</span><span class="n">rollback</span><span class="p">()</span> <span class="k">raise</span> <span class="k">else</span><span class="p">:</span> <span class="n">connection</span><span class="o">.</span><span class="n">commit</span><span class="p">()</span> <span class="n">db</span> <span class="o">=</span> <span class="n">DatabaseConnection</span><span class="p">()</span> <span class="k">with</span> <span class="n">db_transaction</span><span class="p">(</span><span class="n">db</span><span class="p">)</span> <span class="k">as</span> <span class="n">cursor</span><span class="p">:</span> <span class="o">...</span> </pre></div> </div> <p>The <a class="reference internal" href="../library/contextlib.html#module-contextlib" title="contextlib: Utilities for with-statement contexts."><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextlib</span></code></a> module also has a <code class="docutils literal notranslate"><span class="pre">nested(mgr1,</span> <span class="pre">mgr2,</span> <span class="pre">...)</span></code> function that combines a number of context managers so you don’t need to write nested ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statements. In this example, the single ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement both starts a database transaction and acquires a thread lock:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">lock</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Lock</span><span class="p">()</span> <span class="k">with</span> <span class="n">nested</span> <span class="p">(</span><span class="n">db_transaction</span><span class="p">(</span><span class="n">db</span><span class="p">),</span> <span class="n">lock</span><span class="p">)</span> <span class="k">as</span> <span class="p">(</span><span class="n">cursor</span><span class="p">,</span> <span class="n">locked</span><span class="p">):</span> <span class="o">...</span> </pre></div> </div> <p>Finally, the <code class="xref py py-func docutils literal notranslate"><span class="pre">closing()</span></code> function returns its argument so that it can be bound to a variable, and calls the argument’s <code class="docutils literal notranslate"><span class="pre">.close()</span></code> method at the end of the block.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">urllib</span><span class="o">,</span> <span class="nn">sys</span> <span class="kn">from</span> <span class="nn">contextlib</span> <span class="k">import</span> <span class="n">closing</span> <span class="k">with</span> <span class="n">closing</span><span class="p">(</span><span class="n">urllib</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="s1">'http://www.yahoo.com'</span><span class="p">))</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span> <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">f</span><span class="p">:</span> <span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">line</span><span class="p">)</span> </pre></div> </div> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="docutils"> <dt><span class="target" id="index-3"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0343"><strong>PEP 343</strong></a> - The “with” statement</dt> <dd>PEP written by Guido van Rossum and Nick Coghlan; implemented by Mike Bland, Guido van Rossum, and Neal Norwitz. The PEP shows the code generated for a ‘<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a>’ statement, which can be helpful in learning how the statement works.</dd> </dl> <p class="last">The documentation for the <a class="reference internal" href="../library/contextlib.html#module-contextlib" title="contextlib: Utilities for with-statement contexts."><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextlib</span></code></a> module.</p> </div> </div> </div> <div class="section" id="pep-366-explicit-relative-imports-from-a-main-module"> <span id="pep-0366"></span><h2>PEP 366: Explicit Relative Imports From a Main Module<a class="headerlink" href="#pep-366-explicit-relative-imports-from-a-main-module" title="Permalink to this headline">¶</a></h2> <p>Python’s <a class="reference internal" href="../using/cmdline.html#cmdoption-m"><code class="xref std std-option docutils literal notranslate"><span class="pre">-m</span></code></a> switch allows running a module as a script. When you ran a module that was located inside a package, relative imports didn’t work correctly.</p> <p>The fix for Python 2.6 adds a <a class="reference internal" href="../reference/import.html#__package__" title="__package__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__package__</span></code></a> attribute to modules. When this attribute is present, relative imports will be relative to the value of this attribute instead of the <a class="reference internal" href="../reference/import.html#__name__" title="__name__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__name__</span></code></a> attribute.</p> <p>PEP 302-style importers can then set <a class="reference internal" href="../reference/import.html#__package__" title="__package__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__package__</span></code></a> as necessary. The <a class="reference internal" href="../library/runpy.html#module-runpy" title="runpy: Locate and run Python modules without importing them first."><code class="xref py py-mod docutils literal notranslate"><span class="pre">runpy</span></code></a> module that implements the <a class="reference internal" href="../using/cmdline.html#cmdoption-m"><code class="xref std std-option docutils literal notranslate"><span class="pre">-m</span></code></a> switch now does this, so relative imports will now work correctly in scripts running from inside a package.</p> </div> <div class="section" id="pep-370-per-user-site-packages-directory"> <span id="pep-0370"></span><h2>PEP 370: Per-user <code class="docutils literal notranslate"><span class="pre">site-packages</span></code> Directory<a class="headerlink" href="#pep-370-per-user-site-packages-directory" title="Permalink to this headline">¶</a></h2> <p>When you run Python, the module search path <code class="docutils literal notranslate"><span class="pre">sys.path</span></code> usually includes a directory whose path ends in <code class="docutils literal notranslate"><span class="pre">"site-packages"</span></code>. This directory is intended to hold locally-installed packages available to all users using a machine or a particular site installation.</p> <p>Python 2.6 introduces a convention for user-specific site directories. The directory varies depending on the platform:</p> <ul class="simple"> <li>Unix and Mac OS X: <code class="file docutils literal notranslate"><span class="pre">~/.local/</span></code></li> <li>Windows: <code class="file docutils literal notranslate"><span class="pre">%APPDATA%/Python</span></code></li> </ul> <p>Within this directory, there will be version-specific subdirectories, such as <code class="file docutils literal notranslate"><span class="pre">lib/python2.6/site-packages</span></code> on Unix/Mac OS and <code class="file docutils literal notranslate"><span class="pre">Python26/site-packages</span></code> on Windows.</p> <p>If you don’t like the default directory, it can be overridden by an environment variable. <span class="target" id="index-4"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONUSERBASE"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONUSERBASE</span></code></a> sets the root directory used for all Python versions supporting this feature. On Windows, the directory for application-specific data can be changed by setting the <span class="target" id="index-5"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">APPDATA</span></code> environment variable. You can also modify the <code class="file docutils literal notranslate"><span class="pre">site.py</span></code> file for your Python installation.</p> <p>The feature can be disabled entirely by running Python with the <a class="reference internal" href="../using/cmdline.html#cmdoption-s"><code class="xref std std-option docutils literal notranslate"><span class="pre">-s</span></code></a> option or setting the <span class="target" id="index-6"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONNOUSERSITE"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONNOUSERSITE</span></code></a> environment variable.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-7"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0370"><strong>PEP 370</strong></a> - Per-user <code class="docutils literal notranslate"><span class="pre">site-packages</span></code> Directory</dt> <dd>PEP written and implemented by Christian Heimes.</dd> </dl> </div> </div> <div class="section" id="pep-371-the-multiprocessing-package"> <span id="pep-0371"></span><h2>PEP 371: The <code class="docutils literal notranslate"><span class="pre">multiprocessing</span></code> Package<a class="headerlink" href="#pep-371-the-multiprocessing-package" title="Permalink to this headline">¶</a></h2> <p>The new <a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> package lets Python programs create new processes that will perform a computation and return a result to the parent. The parent and child processes can communicate using queues and pipes, synchronize their operations using locks and semaphores, and can share simple arrays of data.</p> <p>The <a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> module started out as an exact emulation of the <a class="reference internal" href="../library/threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> module using processes instead of threads. That goal was discarded along the path to Python 2.6, but the general approach of the module is still similar. The fundamental class is the <code class="xref py py-class docutils literal notranslate"><span class="pre">Process</span></code>, which is passed a callable object and a collection of arguments. The <code class="xref py py-meth docutils literal notranslate"><span class="pre">start()</span></code> method sets the callable running in a subprocess, after which you can call the <code class="xref py py-meth docutils literal notranslate"><span class="pre">is_alive()</span></code> method to check whether the subprocess is still running and the <code class="xref py py-meth docutils literal notranslate"><span class="pre">join()</span></code> method to wait for the process to exit.</p> <p>Here’s a simple example where the subprocess will calculate a factorial. The function doing the calculation is written strangely so that it takes significantly longer when the input argument is a multiple of 4.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">time</span> <span class="kn">from</span> <span class="nn">multiprocessing</span> <span class="k">import</span> <span class="n">Process</span><span class="p">,</span> <span class="n">Queue</span> <span class="k">def</span> <span class="nf">factorial</span><span class="p">(</span><span class="n">queue</span><span class="p">,</span> <span class="n">N</span><span class="p">):</span> <span class="s2">"Compute a factorial."</span> <span class="c1"># If N is a multiple of 4, this function will take much longer.</span> <span class="k">if</span> <span class="p">(</span><span class="n">N</span> <span class="o">%</span> <span class="mi">4</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span> <span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="o">.</span><span class="mi">05</span> <span class="o">*</span> <span class="n">N</span><span class="o">/</span><span class="mi">4</span><span class="p">)</span> <span class="c1"># Calculate the result</span> <span class="n">fact</span> <span class="o">=</span> <span class="mi">1</span><span class="n">L</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p">):</span> <span class="n">fact</span> <span class="o">=</span> <span class="n">fact</span> <span class="o">*</span> <span class="n">i</span> <span class="c1"># Put the result on the queue</span> <span class="n">queue</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="n">fact</span><span class="p">)</span> <span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span> <span class="n">queue</span> <span class="o">=</span> <span class="n">Queue</span><span class="p">()</span> <span class="n">N</span> <span class="o">=</span> <span class="mi">5</span> <span class="n">p</span> <span class="o">=</span> <span class="n">Process</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">factorial</span><span class="p">,</span> <span class="n">args</span><span class="o">=</span><span class="p">(</span><span class="n">queue</span><span class="p">,</span> <span class="n">N</span><span class="p">))</span> <span class="n">p</span><span class="o">.</span><span class="n">start</span><span class="p">()</span> <span class="n">p</span><span class="o">.</span><span class="n">join</span><span class="p">()</span> <span class="n">result</span> <span class="o">=</span> <span class="n">queue</span><span class="o">.</span><span class="n">get</span><span class="p">()</span> <span class="nb">print</span> <span class="s1">'Factorial'</span><span class="p">,</span> <span class="n">N</span><span class="p">,</span> <span class="s1">'='</span><span class="p">,</span> <span class="n">result</span> </pre></div> </div> <p>A <a class="reference internal" href="../library/queue.html#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> is used to communicate the result of the factorial. The <a class="reference internal" href="../library/queue.html#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> object is stored in a global variable. The child process will use the value of the variable when the child was created; because it’s a <a class="reference internal" href="../library/queue.html#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a>, parent and child can use the object to communicate. (If the parent were to change the value of the global variable, the child’s value would be unaffected, and vice versa.)</p> <p>Two other classes, <code class="xref py py-class docutils literal notranslate"><span class="pre">Pool</span></code> and <code class="xref py py-class docutils literal notranslate"><span class="pre">Manager</span></code>, provide higher-level interfaces. <code class="xref py py-class docutils literal notranslate"><span class="pre">Pool</span></code> will create a fixed number of worker processes, and requests can then be distributed to the workers by calling <code class="xref py py-meth docutils literal notranslate"><span class="pre">apply()</span></code> or <code class="xref py py-meth docutils literal notranslate"><span class="pre">apply_async()</span></code> to add a single request, and <a class="reference internal" href="../library/functions.html#map" title="map"><code class="xref py py-meth docutils literal notranslate"><span class="pre">map()</span></code></a> or <code class="xref py py-meth docutils literal notranslate"><span class="pre">map_async()</span></code> to add a number of requests. The following code uses a <code class="xref py py-class docutils literal notranslate"><span class="pre">Pool</span></code> to spread requests across 5 worker processes and retrieve a list of results:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">multiprocessing</span> <span class="k">import</span> <span class="n">Pool</span> <span class="k">def</span> <span class="nf">factorial</span><span class="p">(</span><span class="n">N</span><span class="p">,</span> <span class="n">dictionary</span><span class="p">):</span> <span class="s2">"Compute a factorial."</span> <span class="o">...</span> <span class="n">p</span> <span class="o">=</span> <span class="n">Pool</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span> <span class="n">result</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">map</span><span class="p">(</span><span class="n">factorial</span><span class="p">,</span> <span class="nb">range</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1000</span><span class="p">,</span> <span class="mi">10</span><span class="p">))</span> <span class="k">for</span> <span class="n">v</span> <span class="ow">in</span> <span class="n">result</span><span class="p">:</span> <span class="nb">print</span> <span class="n">v</span> </pre></div> </div> <p>This produces the following output:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="mi">1</span> <span class="mi">39916800</span> <span class="mi">51090942171709440000</span> <span class="mi">8222838654177922817725562880000000</span> <span class="mi">33452526613163807108170062053440751665152000000000</span> <span class="o">...</span> </pre></div> </div> <p>The other high-level interface, the <code class="xref py py-class docutils literal notranslate"><span class="pre">Manager</span></code> class, creates a separate server process that can hold master copies of Python data structures. Other processes can then access and modify these data structures using proxy objects. The following example creates a shared dictionary by calling the <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-meth docutils literal notranslate"><span class="pre">dict()</span></code></a> method; the worker processes then insert values into the dictionary. (Locking is not done for you automatically, which doesn’t matter in this example. <code class="xref py py-class docutils literal notranslate"><span class="pre">Manager</span></code>’s methods also include <code class="xref py py-meth docutils literal notranslate"><span class="pre">Lock()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">RLock()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">Semaphore()</span></code> to create shared locks.)</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">time</span> <span class="kn">from</span> <span class="nn">multiprocessing</span> <span class="k">import</span> <span class="n">Pool</span><span class="p">,</span> <span class="n">Manager</span> <span class="k">def</span> <span class="nf">factorial</span><span class="p">(</span><span class="n">N</span><span class="p">,</span> <span class="n">dictionary</span><span class="p">):</span> <span class="s2">"Compute a factorial."</span> <span class="c1"># Calculate the result</span> <span class="n">fact</span> <span class="o">=</span> <span class="mi">1</span><span class="n">L</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p">):</span> <span class="n">fact</span> <span class="o">=</span> <span class="n">fact</span> <span class="o">*</span> <span class="n">i</span> <span class="c1"># Store result in dictionary</span> <span class="n">dictionary</span><span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="o">=</span> <span class="n">fact</span> <span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span> <span class="n">p</span> <span class="o">=</span> <span class="n">Pool</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span> <span class="n">mgr</span> <span class="o">=</span> <span class="n">Manager</span><span class="p">()</span> <span class="n">d</span> <span class="o">=</span> <span class="n">mgr</span><span class="o">.</span><span class="n">dict</span><span class="p">()</span> <span class="c1"># Create shared dictionary</span> <span class="c1"># Run tasks using the pool</span> <span class="k">for</span> <span class="n">N</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1000</span><span class="p">,</span> <span class="mi">10</span><span class="p">):</span> <span class="n">p</span><span class="o">.</span><span class="n">apply_async</span><span class="p">(</span><span class="n">factorial</span><span class="p">,</span> <span class="p">(</span><span class="n">N</span><span class="p">,</span> <span class="n">d</span><span class="p">))</span> <span class="c1"># Mark pool as closed -- no more tasks can be added.</span> <span class="n">p</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> <span class="c1"># Wait for tasks to exit</span> <span class="n">p</span><span class="o">.</span><span class="n">join</span><span class="p">()</span> <span class="c1"># Output results</span> <span class="k">for</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span> <span class="ow">in</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">items</span><span class="p">()):</span> <span class="nb">print</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span> </pre></div> </div> <p>This will produce the output:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="mi">1</span> <span class="mi">1</span> <span class="mi">11</span> <span class="mi">39916800</span> <span class="mi">21</span> <span class="mi">51090942171709440000</span> <span class="mi">31</span> <span class="mi">8222838654177922817725562880000000</span> <span class="mi">41</span> <span class="mi">33452526613163807108170062053440751665152000000000</span> <span class="mi">51</span> <span class="mf">15511187532873822802242430164693032110632597200169861120000.</span><span class="o">..</span> </pre></div> </div> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <p>The documentation for the <a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> module.</p> <dl class="last docutils"> <dt><span class="target" id="index-8"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0371"><strong>PEP 371</strong></a> - Addition of the multiprocessing package</dt> <dd>PEP written by Jesse Noller and Richard Oudkerk; implemented by Richard Oudkerk and Jesse Noller.</dd> </dl> </div> </div> <div class="section" id="pep-3101-advanced-string-formatting"> <span id="pep-3101"></span><h2>PEP 3101: Advanced String Formatting<a class="headerlink" href="#pep-3101-advanced-string-formatting" title="Permalink to this headline">¶</a></h2> <p>In Python 3.0, the <cite>%</cite> operator is supplemented by a more powerful string formatting method, <a class="reference internal" href="../library/functions.html#format" title="format"><code class="xref py py-meth docutils literal notranslate"><span class="pre">format()</span></code></a>. Support for the <a class="reference internal" href="../library/stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate"><span class="pre">str.format()</span></code></a> method has been backported to Python 2.6.</p> <p>In 2.6, both 8-bit and Unicode strings have a <cite>.format()</cite> method that treats the string as a template and takes the arguments to be formatted. The formatting template uses curly brackets (<cite>{</cite>, <cite>}</cite>) as special characters:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="c1"># Substitute positional argument 0 into the string.</span> <span class="gp">>>> </span><span class="s2">"User ID: </span><span class="si">{0}</span><span class="s2">"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="s2">"root"</span><span class="p">)</span> <span class="go">'User ID: root'</span> <span class="gp">>>> </span><span class="c1"># Use the named keyword arguments</span> <span class="gp">>>> </span><span class="s2">"User ID: </span><span class="si">{uid}</span><span class="s2"> Last seen: </span><span class="si">{last_login}</span><span class="s2">"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span> <span class="gp">... </span> <span class="n">uid</span><span class="o">=</span><span class="s2">"root"</span><span class="p">,</span> <span class="gp">... </span> <span class="n">last_login</span> <span class="o">=</span> <span class="s2">"5 Mar 2008 07:20"</span><span class="p">)</span> <span class="go">'User ID: root Last seen: 5 Mar 2008 07:20'</span> </pre></div> </div> <p>Curly brackets can be escaped by doubling them:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="s2">"Empty dict: {{}}"</span><span class="o">.</span><span class="n">format</span><span class="p">()</span> <span class="go">"Empty dict: {}"</span> </pre></div> </div> <p>Field names can be integers indicating positional arguments, such as <code class="docutils literal notranslate"><span class="pre">{0}</span></code>, <code class="docutils literal notranslate"><span class="pre">{1}</span></code>, etc. or names of keyword arguments. You can also supply compound field names that read attributes or access dictionary keys:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">sys</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="s1">'Platform: </span><span class="si">{0.platform}</span><span class="se">\n</span><span class="s1">Python version: </span><span class="si">{0.version}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">sys</span><span class="p">)</span> <span class="go">Platform: darwin</span> <span class="go">Python version: 2.6a1+ (trunk:61261M, Mar 5 2008, 20:29:41)</span> <span class="go">[GCC 4.0.1 (Apple Computer, Inc. build 5367)]'</span> <span class="gp">>>> </span><span class="kn">import</span> <span class="nn">mimetypes</span> <span class="gp">>>> </span><span class="s1">'Content-type: </span><span class="si">{0[.mp4]}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">mimetypes</span><span class="o">.</span><span class="n">types_map</span><span class="p">)</span> <span class="go">'Content-type: video/mp4'</span> </pre></div> </div> <p>Note that when using dictionary-style notation such as <code class="docutils literal notranslate"><span class="pre">[.mp4]</span></code>, you don’t need to put any quotation marks around the string; it will look up the value using <code class="docutils literal notranslate"><span class="pre">.mp4</span></code> as the key. Strings beginning with a number will be converted to an integer. You can’t write more complicated expressions inside a format string.</p> <p>So far we’ve shown how to specify which field to substitute into the resulting string. The precise formatting used is also controllable by adding a colon followed by a format specifier. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="c1"># Field 0: left justify, pad to 15 characters</span> <span class="gp">>>> </span><span class="c1"># Field 1: right justify, pad to 6 characters</span> <span class="gp">>>> </span><span class="n">fmt</span> <span class="o">=</span> <span class="s1">'</span><span class="si">{0:15}</span><span class="s1"> $</span><span class="si">{1:>6}</span><span class="s1">'</span> <span class="gp">>>> </span><span class="n">fmt</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="s1">'Registration'</span><span class="p">,</span> <span class="mi">35</span><span class="p">)</span> <span class="go">'Registration $ 35'</span> <span class="gp">>>> </span><span class="n">fmt</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="s1">'Tutorial'</span><span class="p">,</span> <span class="mi">50</span><span class="p">)</span> <span class="go">'Tutorial $ 50'</span> <span class="gp">>>> </span><span class="n">fmt</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="s1">'Banquet'</span><span class="p">,</span> <span class="mi">125</span><span class="p">)</span> <span class="go">'Banquet $ 125'</span> </pre></div> </div> <p>Format specifiers can reference other fields through nesting:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">fmt</span> <span class="o">=</span> <span class="s1">'{0:</span><span class="si">{1}</span><span class="s1">}'</span> <span class="gp">>>> </span><span class="n">width</span> <span class="o">=</span> <span class="mi">15</span> <span class="gp">>>> </span><span class="n">fmt</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="s1">'Invoice #1234'</span><span class="p">,</span> <span class="n">width</span><span class="p">)</span> <span class="go">'Invoice #1234 '</span> <span class="gp">>>> </span><span class="n">width</span> <span class="o">=</span> <span class="mi">35</span> <span class="gp">>>> </span><span class="n">fmt</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="s1">'Invoice #1234'</span><span class="p">,</span> <span class="n">width</span><span class="p">)</span> <span class="go">'Invoice #1234 '</span> </pre></div> </div> <p>The alignment of a field within the desired width can be specified:</p> <table border="1" class="docutils"> <colgroup> <col width="27%" /> <col width="73%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Character</th> <th class="head">Effect</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td>< (default)</td> <td>Left-align</td> </tr> <tr class="row-odd"><td>></td> <td>Right-align</td> </tr> <tr class="row-even"><td>^</td> <td>Center</td> </tr> <tr class="row-odd"><td>=</td> <td>(For numeric types only) Pad after the sign.</td> </tr> </tbody> </table> <p>Format specifiers can also include a presentation type, which controls how the value is formatted. For example, floating-point numbers can be formatted as a general number or in exponential notation:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="s1">'</span><span class="si">{0:g}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="mf">3.75</span><span class="p">)</span> <span class="go">'3.75'</span> <span class="gp">>>> </span><span class="s1">'</span><span class="si">{0:e}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="mf">3.75</span><span class="p">)</span> <span class="go">'3.750000e+00'</span> </pre></div> </div> <p>A variety of presentation types are available. Consult the 2.6 documentation for a <a class="reference internal" href="../library/string.html#formatstrings"><span class="std std-ref">complete list</span></a>; here’s a sample:</p> <table border="1" class="docutils"> <colgroup> <col width="6%" /> <col width="94%" /> </colgroup> <tbody valign="top"> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">b</span></code></td> <td>Binary. Outputs the number in base 2.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">c</span></code></td> <td>Character. Converts the integer to the corresponding Unicode character before printing.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">d</span></code></td> <td>Decimal Integer. Outputs the number in base 10.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">o</span></code></td> <td>Octal format. Outputs the number in base 8.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">x</span></code></td> <td>Hex format. Outputs the number in base 16, using lower-case letters for the digits above 9.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">e</span></code></td> <td>Exponent notation. Prints the number in scientific notation using the letter ‘e’ to indicate the exponent.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">g</span></code></td> <td>General format. This prints the number as a fixed-point number, unless the number is too large, in which case it switches to ‘e’ exponent notation.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">n</span></code></td> <td>Number. This is the same as ‘g’ (for floats) or ‘d’ (for integers), except that it uses the current locale setting to insert the appropriate number separator characters.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%</span></code></td> <td>Percentage. Multiplies the number by 100 and displays in fixed (‘f’) format, followed by a percent sign.</td> </tr> </tbody> </table> <p>Classes and types can define a <a class="reference internal" href="../reference/datamodel.html#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__format__()</span></code></a> method to control how they’re formatted. It receives a single argument, the format specifier:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">__format__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">format_spec</span><span class="p">):</span> <span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">format_spec</span><span class="p">,</span> <span class="n">unicode</span><span class="p">):</span> <span class="k">return</span> <span class="n">unicode</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="bp">self</span><span class="p">))</span> <span class="k">else</span><span class="p">:</span> <span class="k">return</span> <span class="nb">str</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span> </pre></div> </div> <p>There’s also a <a class="reference internal" href="../library/functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate"><span class="pre">format()</span></code></a> builtin that will format a single value. It calls the type’s <a class="reference internal" href="../reference/datamodel.html#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__format__()</span></code></a> method with the provided specifier:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">format</span><span class="p">(</span><span class="mf">75.6564</span><span class="p">,</span> <span class="s1">'.2f'</span><span class="p">)</span> <span class="go">'75.66'</span> </pre></div> </div> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><a class="reference internal" href="../library/string.html#formatstrings"><span class="std std-ref">Format String Syntax</span></a></dt> <dd>The reference documentation for format fields.</dd> <dt><span class="target" id="index-9"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3101"><strong>PEP 3101</strong></a> - Advanced String Formatting</dt> <dd>PEP written by Talin. Implemented by Eric Smith.</dd> </dl> </div> </div> <div class="section" id="pep-3105-print-as-a-function"> <span id="pep-3105"></span><h2>PEP 3105: <code class="docutils literal notranslate"><span class="pre">print</span></code> As a Function<a class="headerlink" href="#pep-3105-print-as-a-function" title="Permalink to this headline">¶</a></h2> <p>The <code class="docutils literal notranslate"><span class="pre">print</span></code> statement becomes the <a class="reference internal" href="../library/functions.html#print" title="print"><code class="xref py py-func docutils literal notranslate"><span class="pre">print()</span></code></a> function in Python 3.0. Making <a class="reference internal" href="../library/functions.html#print" title="print"><code class="xref py py-func docutils literal notranslate"><span class="pre">print()</span></code></a> a function makes it possible to replace the function by doing <code class="docutils literal notranslate"><span class="pre">def</span> <span class="pre">print(...)</span></code> or importing a new function from somewhere else.</p> <p>Python 2.6 has a <code class="docutils literal notranslate"><span class="pre">__future__</span></code> import that removes <code class="docutils literal notranslate"><span class="pre">print</span></code> as language syntax, letting you use the functional form instead. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">__future__</span> <span class="k">import</span> <span class="n">print_function</span> <span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="s1">'# of entries'</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">dictionary</span><span class="p">),</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span> </pre></div> </div> <p>The signature of the new function is:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">print</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="n">sep</span><span class="o">=</span><span class="s1">' '</span><span class="p">,</span> <span class="n">end</span><span class="o">=</span><span class="s1">'</span><span class="se">\n</span><span class="s1">'</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span> </pre></div> </div> <p>The parameters are:</p> <blockquote> <div><ul class="simple"> <li><em>args</em>: positional arguments whose values will be printed out.</li> <li><em>sep</em>: the separator, which will be printed between arguments.</li> <li><em>end</em>: the ending text, which will be printed after all of the arguments have been output.</li> <li><em>file</em>: the file object to which the output will be sent.</li> </ul> </div></blockquote> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-10"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3105"><strong>PEP 3105</strong></a> - Make print a function</dt> <dd>PEP written by Georg Brandl.</dd> </dl> </div> </div> <div class="section" id="pep-3110-exception-handling-changes"> <span id="pep-3110"></span><h2>PEP 3110: Exception-Handling Changes<a class="headerlink" href="#pep-3110-exception-handling-changes" title="Permalink to this headline">¶</a></h2> <p>One error that Python programmers occasionally make is writing the following code:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span> <span class="o">...</span> <span class="k">except</span> <span class="ne">TypeError</span><span class="p">,</span> <span class="ne">ValueError</span><span class="p">:</span> <span class="c1"># Wrong!</span> <span class="o">...</span> </pre></div> </div> <p>The author is probably trying to catch both <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> and <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> exceptions, but this code actually does something different: it will catch <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> and bind the resulting exception object to the local name <code class="docutils literal notranslate"><span class="pre">"ValueError"</span></code>. The <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> exception will not be caught at all. The correct code specifies a tuple of exceptions:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span> <span class="o">...</span> <span class="k">except</span> <span class="p">(</span><span class="ne">TypeError</span><span class="p">,</span> <span class="ne">ValueError</span><span class="p">):</span> <span class="o">...</span> </pre></div> </div> <p>This error happens because the use of the comma here is ambiguous: does it indicate two different nodes in the parse tree, or a single node that’s a tuple?</p> <p>Python 3.0 makes this unambiguous by replacing the comma with the word “as”. To catch an exception and store the exception object in the variable <code class="docutils literal notranslate"><span class="pre">exc</span></code>, you must write:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span> <span class="o">...</span> <span class="k">except</span> <span class="ne">TypeError</span> <span class="k">as</span> <span class="n">exc</span><span class="p">:</span> <span class="o">...</span> </pre></div> </div> <p>Python 3.0 will only support the use of “as”, and therefore interprets the first example as catching two different exceptions. Python 2.6 supports both the comma and “as”, so existing code will continue to work. We therefore suggest using “as” when writing new Python code that will only be executed with 2.6.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-11"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3110"><strong>PEP 3110</strong></a> - Catching Exceptions in Python 3000</dt> <dd>PEP written and implemented by Collin Winter.</dd> </dl> </div> </div> <div class="section" id="pep-3112-byte-literals"> <span id="pep-3112"></span><h2>PEP 3112: Byte Literals<a class="headerlink" href="#pep-3112-byte-literals" title="Permalink to this headline">¶</a></h2> <p>Python 3.0 adopts Unicode as the language’s fundamental string type and denotes 8-bit literals differently, either as <code class="docutils literal notranslate"><span class="pre">b'string'</span></code> or using a <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> constructor. For future compatibility, Python 2.6 adds <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> as a synonym for the <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> type, and it also supports the <code class="docutils literal notranslate"><span class="pre">b''</span></code> notation.</p> <p>The 2.6 <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> differs from 3.0’s <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> type in various ways; most notably, the constructor is completely different. In 3.0, <code class="docutils literal notranslate"><span class="pre">bytes([65,</span> <span class="pre">66,</span> <span class="pre">67])</span></code> is 3 elements long, containing the bytes representing <code class="docutils literal notranslate"><span class="pre">ABC</span></code>; in 2.6, <code class="docutils literal notranslate"><span class="pre">bytes([65,</span> <span class="pre">66,</span> <span class="pre">67])</span></code> returns the 12-byte string representing the <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a> of the list.</p> <p>The primary use of <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> in 2.6 will be to write tests of object type such as <code class="docutils literal notranslate"><span class="pre">isinstance(x,</span> <span class="pre">bytes)</span></code>. This will help the 2to3 converter, which can’t tell whether 2.x code intends strings to contain either characters or 8-bit bytes; you can now use either <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> or <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> to represent your intention exactly, and the resulting code will also be correct in Python 3.0.</p> <p>There’s also a <code class="docutils literal notranslate"><span class="pre">__future__</span></code> import that causes all string literals to become Unicode strings. This means that <code class="docutils literal notranslate"><span class="pre">\u</span></code> escape sequences can be used to include Unicode characters:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">__future__</span> <span class="k">import</span> <span class="n">unicode_literals</span> <span class="n">s</span> <span class="o">=</span> <span class="p">(</span><span class="s1">'</span><span class="se">\u751f\u3080\u304e\u3000\u751f\u3054</span><span class="s1">'</span> <span class="s1">'</span><span class="se">\u3081\u3000\u751f\u305f\u307e\u3054</span><span class="s1">'</span><span class="p">)</span> <span class="nb">print</span> <span class="nb">len</span><span class="p">(</span><span class="n">s</span><span class="p">)</span> <span class="c1"># 12 Unicode characters</span> </pre></div> </div> <p>At the C level, Python 3.0 will rename the existing 8-bit string type, called <code class="xref c c-type docutils literal notranslate"><span class="pre">PyStringObject</span></code> in Python 2.x, to <a class="reference internal" href="../c-api/bytes.html#c.PyBytesObject" title="PyBytesObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyBytesObject</span></code></a>. Python 2.6 uses <code class="docutils literal notranslate"><span class="pre">#define</span></code> to support using the names <a class="reference internal" href="../c-api/bytes.html#c.PyBytesObject" title="PyBytesObject"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBytesObject()</span></code></a>, <a class="reference internal" href="../c-api/bytes.html#c.PyBytes_Check" title="PyBytes_Check"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBytes_Check()</span></code></a>, <a class="reference internal" href="../c-api/bytes.html#c.PyBytes_FromStringAndSize" title="PyBytes_FromStringAndSize"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBytes_FromStringAndSize()</span></code></a>, and all the other functions and macros used with strings.</p> <p>Instances of the <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> type are immutable just as strings are. A new <a class="reference internal" href="../library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a> type stores a mutable sequence of bytes:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">bytearray</span><span class="p">([</span><span class="mi">65</span><span class="p">,</span> <span class="mi">66</span><span class="p">,</span> <span class="mi">67</span><span class="p">])</span> <span class="go">bytearray(b'ABC')</span> <span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="nb">bytearray</span><span class="p">(</span><span class="sa">u</span><span class="s1">'</span><span class="se">\u21ef\u3244</span><span class="s1">'</span><span class="p">,</span> <span class="s1">'utf-8'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">b</span> <span class="go">bytearray(b'\xe2\x87\xaf\xe3\x89\x84')</span> <span class="gp">>>> </span><span class="n">b</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'</span><span class="se">\xe3</span><span class="s1">'</span> <span class="gp">>>> </span><span class="n">b</span> <span class="go">bytearray(b'\xe3\x87\xaf\xe3\x89\x84')</span> <span class="gp">>>> </span><span class="n">unicode</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">b</span><span class="p">),</span> <span class="s1">'utf-8'</span><span class="p">)</span> <span class="go">u'\u31ef \u3244'</span> </pre></div> </div> <p>Byte arrays support most of the methods of string types, such as <code class="xref py py-meth docutils literal notranslate"><span class="pre">startswith()</span></code>/<code class="xref py py-meth docutils literal notranslate"><span class="pre">endswith()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">find()</span></code>/<code class="xref py py-meth docutils literal notranslate"><span class="pre">rfind()</span></code>, and some of the methods of lists, such as <code class="xref py py-meth docutils literal notranslate"><span class="pre">append()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">pop()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">reverse()</span></code>.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="nb">bytearray</span><span class="p">(</span><span class="s1">'ABC'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">b</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s1">'d'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">b</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="nb">ord</span><span class="p">(</span><span class="s1">'e'</span><span class="p">))</span> <span class="gp">>>> </span><span class="n">b</span> <span class="go">bytearray(b'ABCde')</span> </pre></div> </div> <p>There’s also a corresponding C API, with <a class="reference internal" href="../c-api/bytearray.html#c.PyByteArray_FromObject" title="PyByteArray_FromObject"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyByteArray_FromObject()</span></code></a>, <a class="reference internal" href="../c-api/bytearray.html#c.PyByteArray_FromStringAndSize" title="PyByteArray_FromStringAndSize"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyByteArray_FromStringAndSize()</span></code></a>, and various other functions.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-12"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3112"><strong>PEP 3112</strong></a> - Bytes literals in Python 3000</dt> <dd>PEP written by Jason Orendorff; backported to 2.6 by Christian Heimes.</dd> </dl> </div> </div> <div class="section" id="pep-3116-new-i-o-library"> <span id="pep-3116"></span><h2>PEP 3116: New I/O Library<a class="headerlink" href="#pep-3116-new-i-o-library" title="Permalink to this headline">¶</a></h2> <p>Python’s built-in file objects support a number of methods, but file-like objects don’t necessarily support all of them. Objects that imitate files usually support <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code>, but they may not support <a class="reference internal" href="../library/readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readline()</span></code></a>, for example. Python 3.0 introduces a layered I/O library in the <a class="reference internal" href="../library/io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module that separates buffering and text-handling features from the fundamental read and write operations.</p> <p>There are three levels of abstract base classes provided by the <a class="reference internal" href="../library/io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module:</p> <ul> <li><p class="first"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code> defines raw I/O operations: <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">tell()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">truncate()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code>. Most of the methods of this class will often map to a single system call. There are also <code class="xref py py-meth docutils literal notranslate"><span class="pre">readable()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">writable()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">seekable()</span></code> methods for determining what operations a given object will allow.</p> <p>Python 3.0 has concrete implementations of this class for files and sockets, but Python 2.6 hasn’t restructured its file and socket objects in this way.</p> </li> <li><p class="first"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code> is an abstract base class that buffers data in memory to reduce the number of system calls used, making I/O processing more efficient. It supports all of the methods of <code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code>, and adds a <code class="xref py py-attr docutils literal notranslate"><span class="pre">raw</span></code> attribute holding the underlying raw object.</p> <p>There are five concrete classes implementing this ABC. <code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code> and <code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code> are for objects that support write-only or read-only usage that have a <code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code> method for random access. <code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRandom</span></code> objects support read and write access upon the same underlying stream, and <code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRWPair</span></code> is for objects such as TTYs that have both read and write operations acting upon unconnected streams of data. The <code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code> class supports reading, writing, and seeking over an in-memory buffer.</p> </li> <li id="index-13"><p class="first"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code>: Provides functions for reading and writing strings (remember, strings will be Unicode in Python 3.0), and supporting <a class="reference internal" href="../glossary.html#term-universal-newlines"><span class="xref std std-term">universal newlines</span></a>. <code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code> defines the <a class="reference internal" href="../library/readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readline()</span></code></a> method and supports iteration upon objects.</p> <p>There are two concrete implementations. <code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOWrapper</span></code> wraps a buffered I/O object, supporting all of the methods for text I/O and adding a <code class="xref py py-attr docutils literal notranslate"><span class="pre">buffer</span></code> attribute for access to the underlying object. <code class="xref py py-class docutils literal notranslate"><span class="pre">StringIO</span></code> simply buffers everything in memory without ever writing anything to disk.</p> <p>(In Python 2.6, <a class="reference internal" href="../library/io.html#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">io.StringIO</span></code></a> is implemented in pure Python, so it’s pretty slow. You should therefore stick with the existing <code class="xref py py-mod docutils literal notranslate"><span class="pre">StringIO</span></code> module or <code class="xref py py-mod docutils literal notranslate"><span class="pre">cStringIO</span></code> for now. At some point Python 3.0’s <a class="reference internal" href="../library/io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module will be rewritten into C for speed, and perhaps the C implementation will be backported to the 2.x releases.)</p> </li> </ul> <p>In Python 2.6, the underlying implementations haven’t been restructured to build on top of the <a class="reference internal" href="../library/io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module’s classes. The module is being provided to make it easier to write code that’s forward-compatible with 3.0, and to save developers the effort of writing their own implementations of buffering and text I/O.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-14"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3116"><strong>PEP 3116</strong></a> - New I/O</dt> <dd>PEP written by Daniel Stutzbach, Mike Verdone, and Guido van Rossum. Code by Guido van Rossum, Georg Brandl, Walter Doerwald, Jeremy Hylton, Martin von Löwis, Tony Lownds, and others.</dd> </dl> </div> </div> <div class="section" id="pep-3118-revised-buffer-protocol"> <span id="pep-3118"></span><h2>PEP 3118: Revised Buffer Protocol<a class="headerlink" href="#pep-3118-revised-buffer-protocol" title="Permalink to this headline">¶</a></h2> <p>The buffer protocol is a C-level API that lets Python types exchange pointers into their internal representations. A memory-mapped file can be viewed as a buffer of characters, for example, and this lets another module such as <a class="reference internal" href="../library/re.html#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> treat memory-mapped files as a string of characters to be searched.</p> <p>The primary users of the buffer protocol are numeric-processing packages such as NumPy, which expose the internal representation of arrays so that callers can write data directly into an array instead of going through a slower API. This PEP updates the buffer protocol in light of experience from NumPy development, adding a number of new features such as indicating the shape of an array or locking a memory region.</p> <p>The most important new C API function is <code class="docutils literal notranslate"><span class="pre">PyObject_GetBuffer(PyObject</span> <span class="pre">*obj,</span> <span class="pre">Py_buffer</span> <span class="pre">*view,</span> <span class="pre">int</span> <span class="pre">flags)</span></code>, which takes an object and a set of flags, and fills in the <code class="docutils literal notranslate"><span class="pre">Py_buffer</span></code> structure with information about the object’s memory representation. Objects can use this operation to lock memory in place while an external caller could be modifying the contents, so there’s a corresponding <code class="docutils literal notranslate"><span class="pre">PyBuffer_Release(Py_buffer</span> <span class="pre">*view)</span></code> to indicate that the external caller is done.</p> <p>The <em>flags</em> argument to <a class="reference internal" href="../c-api/buffer.html#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a> specifies constraints upon the memory returned. Some examples are:</p> <blockquote> <div><ul class="simple"> <li><code class="xref py py-const docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code> indicates that the memory must be writable.</li> <li><code class="xref py py-const docutils literal notranslate"><span class="pre">PyBUF_LOCK</span></code> requests a read-only or exclusive lock on the memory.</li> <li><code class="xref py py-const docutils literal notranslate"><span class="pre">PyBUF_C_CONTIGUOUS</span></code> and <code class="xref py py-const docutils literal notranslate"><span class="pre">PyBUF_F_CONTIGUOUS</span></code> requests a C-contiguous (last dimension varies the fastest) or Fortran-contiguous (first dimension varies the fastest) array layout.</li> </ul> </div></blockquote> <p>Two new argument codes for <a class="reference internal" href="../c-api/arg.html#c.PyArg_ParseTuple" title="PyArg_ParseTuple"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyArg_ParseTuple()</span></code></a>, <code class="docutils literal notranslate"><span class="pre">s*</span></code> and <code class="docutils literal notranslate"><span class="pre">z*</span></code>, return locked buffer objects for a parameter.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-15"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3118"><strong>PEP 3118</strong></a> - Revising the buffer protocol</dt> <dd>PEP written by Travis Oliphant and Carl Banks; implemented by Travis Oliphant.</dd> </dl> </div> </div> <div class="section" id="pep-3119-abstract-base-classes"> <span id="pep-3119"></span><h2>PEP 3119: Abstract Base Classes<a class="headerlink" href="#pep-3119-abstract-base-classes" title="Permalink to this headline">¶</a></h2> <p>Some object-oriented languages such as Java support interfaces, declaring that a class has a given set of methods or supports a given access protocol. Abstract Base Classes (or ABCs) are an equivalent feature for Python. The ABC support consists of an <a class="reference internal" href="../library/abc.html#module-abc" title="abc: Abstract base classes according to PEP 3119."><code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code></a> module containing a metaclass called <code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code>, special handling of this metaclass by the <a class="reference internal" href="../library/functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate"><span class="pre">isinstance()</span></code></a> and <a class="reference internal" href="../library/functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate"><span class="pre">issubclass()</span></code></a> builtins, and a collection of basic ABCs that the Python developers think will be widely useful. Future versions of Python will probably add more ABCs.</p> <p>Let’s say you have a particular class and wish to know whether it supports dictionary-style access. The phrase “dictionary-style” is vague, however. It probably means that accessing items with <code class="docutils literal notranslate"><span class="pre">obj[1]</span></code> works. Does it imply that setting items with <code class="docutils literal notranslate"><span class="pre">obj[2]</span> <span class="pre">=</span> <span class="pre">value</span></code> works? Or that the object will have <code class="xref py py-meth docutils literal notranslate"><span class="pre">keys()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">values()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">items()</span></code> methods? What about the iterative variants such as <code class="xref py py-meth docutils literal notranslate"><span class="pre">iterkeys()</span></code>? <a class="reference internal" href="../library/copy.html#module-copy" title="copy: Shallow and deep copy operations."><code class="xref py py-meth docutils literal notranslate"><span class="pre">copy()</span></code></a> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">update()</span></code>? Iterating over the object with <a class="reference internal" href="../library/functions.html#iter" title="iter"><code class="xref py py-func docutils literal notranslate"><span class="pre">iter()</span></code></a>?</p> <p>The Python 2.6 <a class="reference internal" href="../library/collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate"><span class="pre">collections</span></code></a> module includes a number of different ABCs that represent these distinctions. <code class="xref py py-class docutils literal notranslate"><span class="pre">Iterable</span></code> indicates that a class defines <a class="reference internal" href="../reference/datamodel.html#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__iter__()</span></code></a>, and <code class="xref py py-class docutils literal notranslate"><span class="pre">Container</span></code> means the class defines a <a class="reference internal" href="../reference/datamodel.html#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__contains__()</span></code></a> method and therefore supports <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">in</span> <span class="pre">y</span></code> expressions. The basic dictionary interface of getting items, setting items, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">keys()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">values()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">items()</span></code>, is defined by the <code class="xref py py-class docutils literal notranslate"><span class="pre">MutableMapping</span></code> ABC.</p> <p>You can derive your own classes from a particular ABC to indicate they support that ABC’s interface:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">collections</span> <span class="k">class</span> <span class="nc">Storage</span><span class="p">(</span><span class="n">collections</span><span class="o">.</span><span class="n">MutableMapping</span><span class="p">):</span> <span class="o">...</span> </pre></div> </div> <p>Alternatively, you could write the class without deriving from the desired ABC and instead register the class by calling the ABC’s <code class="xref py py-meth docutils literal notranslate"><span class="pre">register()</span></code> method:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">collections</span> <span class="k">class</span> <span class="nc">Storage</span><span class="p">:</span> <span class="o">...</span> <span class="n">collections</span><span class="o">.</span><span class="n">MutableMapping</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">Storage</span><span class="p">)</span> </pre></div> </div> <p>For classes that you write, deriving from the ABC is probably clearer. The <code class="xref py py-meth docutils literal notranslate"><span class="pre">register()</span></code> method is useful when you’ve written a new ABC that can describe an existing type or class, or if you want to declare that some third-party class implements an ABC. For example, if you defined a <code class="xref py py-class docutils literal notranslate"><span class="pre">PrintableType</span></code> ABC, it’s legal to do:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># Register Python's types</span> <span class="n">PrintableType</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="nb">int</span><span class="p">)</span> <span class="n">PrintableType</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="nb">float</span><span class="p">)</span> <span class="n">PrintableType</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="nb">str</span><span class="p">)</span> </pre></div> </div> <p>Classes should obey the semantics specified by an ABC, but Python can’t check this; it’s up to the class author to understand the ABC’s requirements and to implement the code accordingly.</p> <p>To check whether an object supports a particular interface, you can now write:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">func</span><span class="p">(</span><span class="n">d</span><span class="p">):</span> <span class="k">if</span> <span class="ow">not</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">d</span><span class="p">,</span> <span class="n">collections</span><span class="o">.</span><span class="n">MutableMapping</span><span class="p">):</span> <span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span><span class="s2">"Mapping object expected, not </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="n">d</span><span class="p">)</span> </pre></div> </div> <p>Don’t feel that you must now begin writing lots of checks as in the above example. Python has a strong tradition of duck-typing, where explicit type-checking is never done and code simply calls methods on an object, trusting that those methods will be there and raising an exception if they aren’t. Be judicious in checking for ABCs and only do it where it’s absolutely necessary.</p> <p>You can write your own ABCs by using <code class="docutils literal notranslate"><span class="pre">abc.ABCMeta</span></code> as the metaclass in a class definition:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">abc</span> <span class="k">import</span> <span class="n">ABCMeta</span><span class="p">,</span> <span class="n">abstractmethod</span> <span class="k">class</span> <span class="nc">Drawable</span><span class="p">():</span> <span class="n">__metaclass__</span> <span class="o">=</span> <span class="n">ABCMeta</span> <span class="nd">@abstractmethod</span> <span class="k">def</span> <span class="nf">draw</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">scale</span><span class="o">=</span><span class="mf">1.0</span><span class="p">):</span> <span class="k">pass</span> <span class="k">def</span> <span class="nf">draw_doubled</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">draw</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">scale</span><span class="o">=</span><span class="mf">2.0</span><span class="p">)</span> <span class="k">class</span> <span class="nc">Square</span><span class="p">(</span><span class="n">Drawable</span><span class="p">):</span> <span class="k">def</span> <span class="nf">draw</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">scale</span><span class="p">):</span> <span class="o">...</span> </pre></div> </div> <p>In the <code class="xref py py-class docutils literal notranslate"><span class="pre">Drawable</span></code> ABC above, the <code class="xref py py-meth docutils literal notranslate"><span class="pre">draw_doubled()</span></code> method renders the object at twice its size and can be implemented in terms of other methods described in <code class="xref py py-class docutils literal notranslate"><span class="pre">Drawable</span></code>. Classes implementing this ABC therefore don’t need to provide their own implementation of <code class="xref py py-meth docutils literal notranslate"><span class="pre">draw_doubled()</span></code>, though they can do so. An implementation of <code class="xref py py-meth docutils literal notranslate"><span class="pre">draw()</span></code> is necessary, though; the ABC can’t provide a useful generic implementation.</p> <p>You can apply the <code class="docutils literal notranslate"><span class="pre">@abstractmethod</span></code> decorator to methods such as <code class="xref py py-meth docutils literal notranslate"><span class="pre">draw()</span></code> that must be implemented; Python will then raise an exception for classes that don’t define the method. Note that the exception is only raised when you actually try to create an instance of a subclass lacking the method:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Circle</span><span class="p">(</span><span class="n">Drawable</span><span class="p">):</span> <span class="gp">... </span> <span class="k">pass</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">c</span> <span class="o">=</span> <span class="n">Circle</span><span class="p">()</span> <span class="gt">Traceback (most recent call last):</span> File <span class="nb">"<stdin>"</span>, line <span class="m">1</span>, in <span class="n"><module></span> <span class="gr">TypeError</span>: <span class="n">Can't instantiate abstract class Circle with abstract methods draw</span> <span class="go">>>></span> </pre></div> </div> <p>Abstract data attributes can be declared using the <code class="docutils literal notranslate"><span class="pre">@abstractproperty</span></code> decorator:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">abc</span> <span class="k">import</span> <span class="n">abstractproperty</span> <span class="o">...</span> <span class="nd">@abstractproperty</span> <span class="k">def</span> <span class="nf">readonly</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_x</span> </pre></div> </div> <p>Subclasses must then define a <code class="xref py py-meth docutils literal notranslate"><span class="pre">readonly()</span></code> property.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-16"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3119"><strong>PEP 3119</strong></a> - Introducing Abstract Base Classes</dt> <dd>PEP written by Guido van Rossum and Talin. Implemented by Guido van Rossum. Backported to 2.6 by Benjamin Aranguren, with Alex Martelli.</dd> </dl> </div> </div> <div class="section" id="pep-3127-integer-literal-support-and-syntax"> <span id="pep-3127"></span><h2>PEP 3127: Integer Literal Support and Syntax<a class="headerlink" href="#pep-3127-integer-literal-support-and-syntax" title="Permalink to this headline">¶</a></h2> <p>Python 3.0 changes the syntax for octal (base-8) integer literals, prefixing them with “0o” or “0O” instead of a leading zero, and adds support for binary (base-2) integer literals, signalled by a “0b” or “0B” prefix.</p> <p>Python 2.6 doesn’t drop support for a leading 0 signalling an octal number, but it does add support for “0o” and “0b”:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="mo">0o21</span><span class="p">,</span> <span class="mi">2</span><span class="o">*</span><span class="mi">8</span> <span class="o">+</span> <span class="mi">1</span> <span class="go">(17, 17)</span> <span class="gp">>>> </span><span class="mb">0b101111</span> <span class="go">47</span> </pre></div> </div> <p>The <a class="reference internal" href="../library/functions.html#oct" title="oct"><code class="xref py py-func docutils literal notranslate"><span class="pre">oct()</span></code></a> builtin still returns numbers prefixed with a leading zero, and a new <a class="reference internal" href="../library/functions.html#bin" title="bin"><code class="xref py py-func docutils literal notranslate"><span class="pre">bin()</span></code></a> builtin returns the binary representation for a number:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">oct</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span> <span class="go">'052'</span> <span class="gp">>>> </span><span class="n">future_builtins</span><span class="o">.</span><span class="n">oct</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span> <span class="go">'0o52'</span> <span class="gp">>>> </span><span class="nb">bin</span><span class="p">(</span><span class="mi">173</span><span class="p">)</span> <span class="go">'0b10101101'</span> </pre></div> </div> <p>The <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-func docutils literal notranslate"><span class="pre">int()</span></code></a> and <code class="xref py py-func docutils literal notranslate"><span class="pre">long()</span></code> builtins will now accept the “0o” and “0b” prefixes when base-8 or base-2 are requested, or when the <em>base</em> argument is zero (signalling that the base used should be determined from the string):</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">int</span> <span class="p">(</span><span class="s1">'0o52'</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span> <span class="go">42</span> <span class="gp">>>> </span><span class="nb">int</span><span class="p">(</span><span class="s1">'1101'</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span> <span class="go">13</span> <span class="gp">>>> </span><span class="nb">int</span><span class="p">(</span><span class="s1">'0b1101'</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span> <span class="go">13</span> <span class="gp">>>> </span><span class="nb">int</span><span class="p">(</span><span class="s1">'0b1101'</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span> <span class="go">13</span> </pre></div> </div> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-17"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3127"><strong>PEP 3127</strong></a> - Integer Literal Support and Syntax</dt> <dd>PEP written by Patrick Maupin; backported to 2.6 by Eric Smith.</dd> </dl> </div> </div> <div class="section" id="pep-3129-class-decorators"> <span id="pep-3129"></span><h2>PEP 3129: Class Decorators<a class="headerlink" href="#pep-3129-class-decorators" title="Permalink to this headline">¶</a></h2> <p>Decorators have been extended from functions to classes. It’s now legal to write:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="nd">@foo</span> <span class="nd">@bar</span> <span class="k">class</span> <span class="nc">A</span><span class="p">:</span> <span class="k">pass</span> </pre></div> </div> <p>This is equivalent to:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">A</span><span class="p">:</span> <span class="k">pass</span> <span class="n">A</span> <span class="o">=</span> <span class="n">foo</span><span class="p">(</span><span class="n">bar</span><span class="p">(</span><span class="n">A</span><span class="p">))</span> </pre></div> </div> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt><span class="target" id="index-18"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3129"><strong>PEP 3129</strong></a> - Class Decorators</dt> <dd>PEP written by Collin Winter.</dd> </dl> </div> </div> <div class="section" id="pep-3141-a-type-hierarchy-for-numbers"> <span id="pep-3141"></span><h2>PEP 3141: A Type Hierarchy for Numbers<a class="headerlink" href="#pep-3141-a-type-hierarchy-for-numbers" title="Permalink to this headline">¶</a></h2> <p>Python 3.0 adds several abstract base classes for numeric types inspired by Scheme’s numeric tower. These classes were backported to 2.6 as the <a class="reference internal" href="../library/numbers.html#module-numbers" title="numbers: Numeric abstract base classes (Complex, Real, Integral, etc.)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">numbers</span></code></a> module.</p> <p>The most general ABC is <code class="xref py py-class docutils literal notranslate"><span class="pre">Number</span></code>. It defines no operations at all, and only exists to allow checking if an object is a number by doing <code class="docutils literal notranslate"><span class="pre">isinstance(obj,</span> <span class="pre">Number)</span></code>.</p> <p><code class="xref py py-class docutils literal notranslate"><span class="pre">Complex</span></code> is a subclass of <code class="xref py py-class docutils literal notranslate"><span class="pre">Number</span></code>. Complex numbers can undergo the basic operations of addition, subtraction, multiplication, division, and exponentiation, and you can retrieve the real and imaginary parts and obtain a number’s conjugate. Python’s built-in complex type is an implementation of <code class="xref py py-class docutils literal notranslate"><span class="pre">Complex</span></code>.</p> <p><code class="xref py py-class docutils literal notranslate"><span class="pre">Real</span></code> further derives from <code class="xref py py-class docutils literal notranslate"><span class="pre">Complex</span></code>, and adds operations that only work on real numbers: <code class="xref py py-func docutils literal notranslate"><span class="pre">floor()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">trunc()</span></code>, rounding, taking the remainder mod N, floor division, and comparisons.</p> <p><code class="xref py py-class docutils literal notranslate"><span class="pre">Rational</span></code> numbers derive from <code class="xref py py-class docutils literal notranslate"><span class="pre">Real</span></code>, have <code class="xref py py-attr docutils literal notranslate"><span class="pre">numerator</span></code> and <code class="xref py py-attr docutils literal notranslate"><span class="pre">denominator</span></code> properties, and can be converted to floats. Python 2.6 adds a simple rational-number class, <code class="xref py py-class docutils literal notranslate"><span class="pre">Fraction</span></code>, in the <a class="reference internal" href="../library/fractions.html#module-fractions" title="fractions: Rational numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">fractions</span></code></a> module. (It’s called <code class="xref py py-class docutils literal notranslate"><span class="pre">Fraction</span></code> instead of <code class="xref py py-class docutils literal notranslate"><span class="pre">Rational</span></code> to avoid a name clash with <a class="reference internal" href="../library/numbers.html#numbers.Rational" title="numbers.Rational"><code class="xref py py-class docutils literal notranslate"><span class="pre">numbers.Rational</span></code></a>.)</p> <p><code class="xref py py-class docutils literal notranslate"><span class="pre">Integral</span></code> numbers derive from <code class="xref py py-class docutils literal notranslate"><span class="pre">Rational</span></code>, and can be shifted left and right with <code class="docutils literal notranslate"><span class="pre"><<</span></code> and <code class="docutils literal notranslate"><span class="pre">>></span></code>, combined using bitwise operations such as <code class="docutils literal notranslate"><span class="pre">&</span></code> and <code class="docutils literal notranslate"><span class="pre">|</span></code>, and can be used as array indexes and slice boundaries.</p> <p>In Python 3.0, the PEP slightly redefines the existing builtins <a class="reference internal" href="../library/functions.html#round" title="round"><code class="xref py py-func docutils literal notranslate"><span class="pre">round()</span></code></a>, <a class="reference internal" href="../library/math.html#math.floor" title="math.floor"><code class="xref py py-func docutils literal notranslate"><span class="pre">math.floor()</span></code></a>, <a class="reference internal" href="../library/math.html#math.ceil" title="math.ceil"><code class="xref py py-func docutils literal notranslate"><span class="pre">math.ceil()</span></code></a>, and adds a new one, <a class="reference internal" href="../library/math.html#math.trunc" title="math.trunc"><code class="xref py py-func docutils literal notranslate"><span class="pre">math.trunc()</span></code></a>, that’s been backported to Python 2.6. <a class="reference internal" href="../library/math.html#math.trunc" title="math.trunc"><code class="xref py py-func docutils literal notranslate"><span class="pre">math.trunc()</span></code></a> rounds toward zero, returning the closest <code class="xref py py-class docutils literal notranslate"><span class="pre">Integral</span></code> that’s between the function’s argument and zero.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="docutils"> <dt><span class="target" id="index-19"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3141"><strong>PEP 3141</strong></a> - A Type Hierarchy for Numbers</dt> <dd>PEP written by Jeffrey Yasskin.</dd> </dl> <p><a class="reference external" href="https://www.gnu.org/software/guile/manual/html_node/Numerical-Tower.html#Numerical-Tower">Scheme’s numerical tower</a>, from the Guile manual.</p> <p class="last"><a class="reference external" href="http://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-9.html#%_sec_6.2">Scheme’s number datatypes</a> from the R5RS Scheme specification.</p> </div> <div class="section" id="the-fractions-module"> <h3>The <a class="reference internal" href="../library/fractions.html#module-fractions" title="fractions: Rational numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">fractions</span></code></a> Module<a class="headerlink" href="#the-fractions-module" title="Permalink to this headline">¶</a></h3> <p>To fill out the hierarchy of numeric types, the <a class="reference internal" href="../library/fractions.html#module-fractions" title="fractions: Rational numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">fractions</span></code></a> module provides a rational-number class. Rational numbers store their values as a numerator and denominator forming a fraction, and can exactly represent numbers such as <code class="docutils literal notranslate"><span class="pre">2/3</span></code> that floating-point numbers can only approximate.</p> <p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">Fraction</span></code> constructor takes two <code class="xref py py-class docutils literal notranslate"><span class="pre">Integral</span></code> values that will be the numerator and denominator of the resulting fraction.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">fractions</span> <span class="k">import</span> <span class="n">Fraction</span> <span class="gp">>>> </span><span class="n">a</span> <span class="o">=</span> <span class="n">Fraction</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="n">Fraction</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">)</span> <span class="gp">>>> </span><span class="nb">float</span><span class="p">(</span><span class="n">a</span><span class="p">),</span> <span class="nb">float</span><span class="p">(</span><span class="n">b</span><span class="p">)</span> <span class="go">(0.66666666666666663, 0.40000000000000002)</span> <span class="gp">>>> </span><span class="n">a</span><span class="o">+</span><span class="n">b</span> <span class="go">Fraction(16, 15)</span> <span class="gp">>>> </span><span class="n">a</span><span class="o">/</span><span class="n">b</span> <span class="go">Fraction(5, 3)</span> </pre></div> </div> <p>For converting floating-point numbers to rationals, the float type now has an <code class="xref py py-meth docutils literal notranslate"><span class="pre">as_integer_ratio()</span></code> method that returns the numerator and denominator for a fraction that evaluates to the same floating-point value:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="p">(</span><span class="mf">2.5</span><span class="p">)</span> <span class="o">.</span><span class="n">as_integer_ratio</span><span class="p">()</span> <span class="go">(5, 2)</span> <span class="gp">>>> </span><span class="p">(</span><span class="mf">3.1415</span><span class="p">)</span> <span class="o">.</span><span class="n">as_integer_ratio</span><span class="p">()</span> <span class="go">(7074029114692207L, 2251799813685248L)</span> <span class="gp">>>> </span><span class="p">(</span><span class="mf">1.</span><span class="o">/</span><span class="mi">3</span><span class="p">)</span> <span class="o">.</span><span class="n">as_integer_ratio</span><span class="p">()</span> <span class="go">(6004799503160661L, 18014398509481984L)</span> </pre></div> </div> <p>Note that values that can only be approximated by floating-point numbers, such as 1./3, are not simplified to the number being approximated; the fraction attempts to match the floating-point value <strong>exactly</strong>.</p> <p>The <a class="reference internal" href="../library/fractions.html#module-fractions" title="fractions: Rational numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">fractions</span></code></a> module is based upon an implementation by Sjoerd Mullender that was in Python’s <code class="file docutils literal notranslate"><span class="pre">Demo/classes/</span></code> directory for a long time. This implementation was significantly updated by Jeffrey Yasskin.</p> </div> </div> <div class="section" id="other-language-changes"> <h2>Other Language Changes<a class="headerlink" href="#other-language-changes" title="Permalink to this headline">¶</a></h2> <p>Some smaller changes made to the core Python language are:</p> <ul> <li><p class="first">Directories and zip archives containing a <code class="file docutils literal notranslate"><span class="pre">__main__.py</span></code> file can now be executed directly by passing their name to the interpreter. The directory or zip archive is automatically inserted as the first entry in sys.path. (Suggestion and initial patch by Andy Chu, subsequently revised by Phillip J. Eby and Nick Coghlan; <a class="reference external" href="https://bugs.python.org/issue1739468">bpo-1739468</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate"><span class="pre">hasattr()</span></code></a> function was catching and ignoring all errors, under the assumption that they meant a <a class="reference internal" href="../reference/datamodel.html#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattr__()</span></code></a> method was failing somehow and the return value of <a class="reference internal" href="../library/functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate"><span class="pre">hasattr()</span></code></a> would therefore be <code class="docutils literal notranslate"><span class="pre">False</span></code>. This logic shouldn’t be applied to <a class="reference internal" href="../library/exceptions.html#KeyboardInterrupt" title="KeyboardInterrupt"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyboardInterrupt</span></code></a> and <a class="reference internal" href="../library/exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a>, however; Python 2.6 will no longer discard such exceptions when <a class="reference internal" href="../library/functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate"><span class="pre">hasattr()</span></code></a> encounters them. (Fixed by Benjamin Peterson; <a class="reference external" href="https://bugs.python.org/issue2196">bpo-2196</a>.)</p> </li> <li><p class="first">When calling a function using the <code class="docutils literal notranslate"><span class="pre">**</span></code> syntax to provide keyword arguments, you are no longer required to use a Python dictionary; any mapping will now work:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">f</span><span class="p">(</span><span class="o">**</span><span class="n">kw</span><span class="p">):</span> <span class="gp">... </span> <span class="nb">print</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">kw</span><span class="p">)</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">ud</span><span class="o">=</span><span class="n">UserDict</span><span class="o">.</span><span class="n">UserDict</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">ud</span><span class="p">[</span><span class="s1">'a'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">1</span> <span class="gp">>>> </span><span class="n">ud</span><span class="p">[</span><span class="s1">'b'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'string'</span> <span class="gp">>>> </span><span class="n">f</span><span class="p">(</span><span class="o">**</span><span class="n">ud</span><span class="p">)</span> <span class="go">['a', 'b']</span> </pre></div> </div> <p>(Contributed by Alexander Belopolsky; <a class="reference external" href="https://bugs.python.org/issue1686487">bpo-1686487</a>.)</p> <p>It’s also become legal to provide keyword arguments after a <code class="docutils literal notranslate"><span class="pre">*args</span></code> argument to a function call.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">f</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">):</span> <span class="gp">... </span> <span class="nb">print</span> <span class="n">args</span><span class="p">,</span> <span class="n">kw</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">f</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span> <span class="o">*</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">),</span> <span class="n">keyword</span><span class="o">=</span><span class="mi">13</span><span class="p">)</span> <span class="go">(1, 2, 3, 4, 5, 6) {'keyword': 13}</span> </pre></div> </div> <p>Previously this would have been a syntax error. (Contributed by Amaury Forgeot d’Arc; <a class="reference external" href="https://bugs.python.org/issue3473">bpo-3473</a>.)</p> </li> <li><p class="first">A new builtin, <code class="docutils literal notranslate"><span class="pre">next(iterator,</span> <span class="pre">[default])</span></code> returns the next item from the specified iterator. If the <em>default</em> argument is supplied, it will be returned if <em>iterator</em> has been exhausted; otherwise, the <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception will be raised. (Backported in <a class="reference external" href="https://bugs.python.org/issue2719">bpo-2719</a>.)</p> </li> <li><p class="first">Tuples now have <code class="xref py py-meth docutils literal notranslate"><span class="pre">index()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">count()</span></code> methods matching the list type’s <code class="xref py py-meth docutils literal notranslate"><span class="pre">index()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">count()</span></code> methods:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">t</span> <span class="o">=</span> <span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">t</span><span class="o">.</span><span class="n">index</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span> <span class="go">3</span> <span class="gp">>>> </span><span class="n">t</span><span class="o">.</span><span class="n">count</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="go">2</span> </pre></div> </div> <p>(Contributed by Raymond Hettinger)</p> </li> <li><p class="first">The built-in types now have improved support for extended slicing syntax, accepting various combinations of <code class="docutils literal notranslate"><span class="pre">(start,</span> <span class="pre">stop,</span> <span class="pre">step)</span></code>. Previously, the support was partial and certain corner cases wouldn’t work. (Implemented by Thomas Wouters.)</p> </li> <li><p class="first">Properties now have three attributes, <code class="xref py py-attr docutils literal notranslate"><span class="pre">getter</span></code>, <code class="xref py py-attr docutils literal notranslate"><span class="pre">setter</span></code> and <code class="xref py py-attr docutils literal notranslate"><span class="pre">deleter</span></code>, that are decorators providing useful shortcuts for adding a getter, setter or deleter function to an existing property. You would use them like this:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="nd">@property</span> <span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_x</span> <span class="nd">@x</span><span class="o">.</span><span class="n">setter</span> <span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">_x</span> <span class="o">=</span> <span class="n">value</span> <span class="nd">@x</span><span class="o">.</span><span class="n">deleter</span> <span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">del</span> <span class="bp">self</span><span class="o">.</span><span class="n">_x</span> <span class="k">class</span> <span class="nc">D</span><span class="p">(</span><span class="n">C</span><span class="p">):</span> <span class="nd">@C</span><span class="o">.</span><span class="n">x</span><span class="o">.</span><span class="n">getter</span> <span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_x</span> <span class="o">*</span> <span class="mi">2</span> <span class="nd">@x</span><span class="o">.</span><span class="n">setter</span> <span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">_x</span> <span class="o">=</span> <span class="n">value</span> <span class="o">/</span> <span class="mi">2</span> </pre></div> </div> </li> <li><p class="first">Several methods of the built-in set types now accept multiple iterables: <code class="xref py py-meth docutils literal notranslate"><span class="pre">intersection()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">intersection_update()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">union()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">update()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">difference()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">difference_update()</span></code>.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">s</span><span class="o">=</span><span class="nb">set</span><span class="p">(</span><span class="s1">'1234567890'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">intersection</span><span class="p">(</span><span class="s1">'abc123'</span><span class="p">,</span> <span class="s1">'cdf246'</span><span class="p">)</span> <span class="c1"># Intersection between all inputs</span> <span class="go">set(['2'])</span> <span class="gp">>>> </span><span class="n">s</span><span class="o">.</span><span class="n">difference</span><span class="p">(</span><span class="s1">'246'</span><span class="p">,</span> <span class="s1">'789'</span><span class="p">)</span> <span class="go">set(['1', '0', '3', '5'])</span> </pre></div> </div> <p>(Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">Many floating-point features were added. The <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-func docutils literal notranslate"><span class="pre">float()</span></code></a> function will now turn the string <code class="docutils literal notranslate"><span class="pre">nan</span></code> into an IEEE 754 Not A Number value, and <code class="docutils literal notranslate"><span class="pre">+inf</span></code> and <code class="docutils literal notranslate"><span class="pre">-inf</span></code> into positive or negative infinity. This works on any platform with IEEE 754 semantics. (Contributed by Christian Heimes; <a class="reference external" href="https://bugs.python.org/issue1635">bpo-1635</a>.)</p> <p>Other functions in the <a class="reference internal" href="../library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">math</span></code></a> module, <code class="xref py py-func docutils literal notranslate"><span class="pre">isinf()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">isnan()</span></code>, return true if their floating-point argument is infinite or Not A Number. (<a class="reference external" href="https://bugs.python.org/issue1640">bpo-1640</a>)</p> <p>Conversion functions were added to convert floating-point numbers into hexadecimal strings (<a class="reference external" href="https://bugs.python.org/issue3008">bpo-3008</a>). These functions convert floats to and from a string representation without introducing rounding errors from the conversion between decimal and binary. Floats have a <a class="reference internal" href="../library/functions.html#hex" title="hex"><code class="xref py py-meth docutils literal notranslate"><span class="pre">hex()</span></code></a> method that returns a string representation, and the <code class="docutils literal notranslate"><span class="pre">float.fromhex()</span></code> method converts a string back into a number:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">a</span> <span class="o">=</span> <span class="mf">3.75</span> <span class="gp">>>> </span><span class="n">a</span><span class="o">.</span><span class="n">hex</span><span class="p">()</span> <span class="go">'0x1.e000000000000p+1'</span> <span class="gp">>>> </span><span class="nb">float</span><span class="o">.</span><span class="n">fromhex</span><span class="p">(</span><span class="s1">'0x1.e000000000000p+1'</span><span class="p">)</span> <span class="go">3.75</span> <span class="gp">>>> </span><span class="n">b</span><span class="o">=</span><span class="mf">1.</span><span class="o">/</span><span class="mi">3</span> <span class="gp">>>> </span><span class="n">b</span><span class="o">.</span><span class="n">hex</span><span class="p">()</span> <span class="go">'0x1.5555555555555p-2'</span> </pre></div> </div> </li> <li><p class="first">A numerical nicety: when creating a complex number from two floats on systems that support signed zeros (-0 and +0), the <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-func docutils literal notranslate"><span class="pre">complex()</span></code></a> constructor will now preserve the sign of the zero. (Fixed by Mark T. Dickinson; <a class="reference external" href="https://bugs.python.org/issue1507">bpo-1507</a>.)</p> </li> <li><p class="first">Classes that inherit a <a class="reference internal" href="../reference/datamodel.html#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__hash__()</span></code></a> method from a parent class can set <code class="docutils literal notranslate"><span class="pre">__hash__</span> <span class="pre">=</span> <span class="pre">None</span></code> to indicate that the class isn’t hashable. This will make <code class="docutils literal notranslate"><span class="pre">hash(obj)</span></code> raise a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> and the class will not be indicated as implementing the <code class="xref py py-class docutils literal notranslate"><span class="pre">Hashable</span></code> ABC.</p> <p>You should do this when you’ve defined a <code class="xref py py-meth docutils literal notranslate"><span class="pre">__cmp__()</span></code> or <a class="reference internal" href="../reference/datamodel.html#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__eq__()</span></code></a> method that compares objects by their value rather than by identity. All objects have a default hash method that uses <code class="docutils literal notranslate"><span class="pre">id(obj)</span></code> as the hash value. There’s no tidy way to remove the <a class="reference internal" href="../reference/datamodel.html#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__hash__()</span></code></a> method inherited from a parent class, so assigning <code class="docutils literal notranslate"><span class="pre">None</span></code> was implemented as an override. At the C level, extensions can set <code class="docutils literal notranslate"><span class="pre">tp_hash</span></code> to <a class="reference internal" href="../c-api/object.html#c.PyObject_HashNotImplemented" title="PyObject_HashNotImplemented"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_HashNotImplemented()</span></code></a>. (Fixed by Nick Coghlan and Amaury Forgeot d’Arc; <a class="reference external" href="https://bugs.python.org/issue2235">bpo-2235</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/exceptions.html#GeneratorExit" title="GeneratorExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code></a> exception now subclasses <a class="reference internal" href="../library/exceptions.html#BaseException" title="BaseException"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BaseException</span></code></a> instead of <a class="reference internal" href="../library/exceptions.html#Exception" title="Exception"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Exception</span></code></a>. This means that an exception handler that does <code class="docutils literal notranslate"><span class="pre">except</span> <span class="pre">Exception:</span></code> will not inadvertently catch <a class="reference internal" href="../library/exceptions.html#GeneratorExit" title="GeneratorExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code></a>. (Contributed by Chad Austin; <a class="reference external" href="https://bugs.python.org/issue1537">bpo-1537</a>.)</p> </li> <li><p class="first">Generator objects now have a <code class="xref py py-attr docutils literal notranslate"><span class="pre">gi_code</span></code> attribute that refers to the original code object backing the generator. (Contributed by Collin Winter; <a class="reference external" href="https://bugs.python.org/issue1473257">bpo-1473257</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/functions.html#compile" title="compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">compile()</span></code></a> built-in function now accepts keyword arguments as well as positional parameters. (Contributed by Thomas Wouters; <a class="reference external" href="https://bugs.python.org/issue1444529">bpo-1444529</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-func docutils literal notranslate"><span class="pre">complex()</span></code></a> constructor now accepts strings containing parenthesized complex numbers, meaning that <code class="docutils literal notranslate"><span class="pre">complex(repr(cplx))</span></code> will now round-trip values. For example, <code class="docutils literal notranslate"><span class="pre">complex('(3+4j)')</span></code> now returns the value (3+4j). (<a class="reference external" href="https://bugs.python.org/issue1491866">bpo-1491866</a>)</p> </li> <li><p class="first">The string <code class="xref py py-meth docutils literal notranslate"><span class="pre">translate()</span></code> method now accepts <code class="docutils literal notranslate"><span class="pre">None</span></code> as the translation table parameter, which is treated as the identity transformation. This makes it easier to carry out operations that only delete characters. (Contributed by Bengt Richter and implemented by Raymond Hettinger; <a class="reference external" href="https://bugs.python.org/issue1193128">bpo-1193128</a>.)</p> </li> <li><p class="first">The built-in <a class="reference internal" href="../library/functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate"><span class="pre">dir()</span></code></a> function now checks for a <a class="reference internal" href="../reference/datamodel.html#object.__dir__" title="object.__dir__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__dir__()</span></code></a> method on the objects it receives. This method must return a list of strings containing the names of valid attributes for the object, and lets the object control the value that <a class="reference internal" href="../library/functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate"><span class="pre">dir()</span></code></a> produces. Objects that have <a class="reference internal" href="../reference/datamodel.html#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattr__()</span></code></a> or <a class="reference internal" href="../reference/datamodel.html#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattribute__()</span></code></a> methods can use this to advertise pseudo-attributes they will honor. (<a class="reference external" href="https://bugs.python.org/issue1591665">bpo-1591665</a>)</p> </li> <li><p class="first">Instance method objects have new attributes for the object and function comprising the method; the new synonym for <code class="xref py py-attr docutils literal notranslate"><span class="pre">im_self</span></code> is <code class="xref py py-attr docutils literal notranslate"><span class="pre">__self__</span></code>, and <code class="xref py py-attr docutils literal notranslate"><span class="pre">im_func</span></code> is also available as <code class="xref py py-attr docutils literal notranslate"><span class="pre">__func__</span></code>. The old names are still supported in Python 2.6, but are gone in 3.0.</p> </li> <li><p class="first">An obscure change: when you use the <a class="reference internal" href="../library/functions.html#locals" title="locals"><code class="xref py py-func docutils literal notranslate"><span class="pre">locals()</span></code></a> function inside a <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">class</span></code></a> statement, the resulting dictionary no longer returns free variables. (Free variables, in this case, are variables referenced in the <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">class</span></code></a> statement that aren’t attributes of the class.)</p> </li> </ul> <div class="section" id="optimizations"> <h3>Optimizations<a class="headerlink" href="#optimizations" title="Permalink to this headline">¶</a></h3> <ul> <li><p class="first">The <a class="reference internal" href="../library/warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate"><span class="pre">warnings</span></code></a> module has been rewritten in C. This makes it possible to invoke warnings from the parser, and may also make the interpreter’s startup faster. (Contributed by Neal Norwitz and Brett Cannon; <a class="reference external" href="https://bugs.python.org/issue1631171">bpo-1631171</a>.)</p> </li> <li><p class="first">Type objects now have a cache of methods that can reduce the work required to find the correct method implementation for a particular class; once cached, the interpreter doesn’t need to traverse base classes to figure out the right method to call. The cache is cleared if a base class or the class itself is modified, so the cache should remain correct even in the face of Python’s dynamic nature. (Original optimization implemented by Armin Rigo, updated for Python 2.6 by Kevin Jacobs; <a class="reference external" href="https://bugs.python.org/issue1700288">bpo-1700288</a>.)</p> <p>By default, this change is only applied to types that are included with the Python core. Extension modules may not necessarily be compatible with this cache, so they must explicitly add <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_TPFLAGS_HAVE_VERSION_TAG</span></code> to the module’s <code class="docutils literal notranslate"><span class="pre">tp_flags</span></code> field to enable the method cache. (To be compatible with the method cache, the extension module’s code must not directly access and modify the <code class="docutils literal notranslate"><span class="pre">tp_dict</span></code> member of any of the types it implements. Most modules don’t do this, but it’s impossible for the Python interpreter to determine that. See <a class="reference external" href="https://bugs.python.org/issue1878">bpo-1878</a> for some discussion.)</p> </li> <li><p class="first">Function calls that use keyword arguments are significantly faster by doing a quick pointer comparison, usually saving the time of a full string comparison. (Contributed by Raymond Hettinger, after an initial implementation by Antoine Pitrou; <a class="reference external" href="https://bugs.python.org/issue1819">bpo-1819</a>.)</p> </li> <li><p class="first">All of the functions in the <a class="reference internal" href="../library/struct.html#module-struct" title="struct: Interpret bytes as packed binary data."><code class="xref py py-mod docutils literal notranslate"><span class="pre">struct</span></code></a> module have been rewritten in C, thanks to work at the Need For Speed sprint. (Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">Some of the standard built-in types now set a bit in their type objects. This speeds up checking whether an object is a subclass of one of these types. (Contributed by Neal Norwitz.)</p> </li> <li><p class="first">Unicode strings now use faster code for detecting whitespace and line breaks; this speeds up the <code class="xref py py-meth docutils literal notranslate"><span class="pre">split()</span></code> method by about 25% and <code class="xref py py-meth docutils literal notranslate"><span class="pre">splitlines()</span></code> by 35%. (Contributed by Antoine Pitrou.) Memory usage is reduced by using pymalloc for the Unicode string’s data.</p> </li> <li><p class="first">The <code class="docutils literal notranslate"><span class="pre">with</span></code> statement now stores the <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__exit__()</span></code></a> method on the stack, producing a small speedup. (Implemented by Jeffrey Yasskin.)</p> </li> <li><p class="first">To reduce memory usage, the garbage collector will now clear internal free lists when garbage-collecting the highest generation of objects. This may return memory to the operating system sooner.</p> </li> </ul> </div> <div class="section" id="interpreter-changes"> <span id="new-26-interpreter"></span><h3>Interpreter Changes<a class="headerlink" href="#interpreter-changes" title="Permalink to this headline">¶</a></h3> <p>Two command-line options have been reserved for use by other Python implementations. The <a class="reference internal" href="../using/cmdline.html#cmdoption-j"><code class="xref std std-option docutils literal notranslate"><span class="pre">-J</span></code></a> switch has been reserved for use by Jython for Jython-specific options, such as switches that are passed to the underlying JVM. <a class="reference internal" href="../using/cmdline.html#id5"><code class="xref std std-option docutils literal notranslate"><span class="pre">-X</span></code></a> has been reserved for options specific to a particular implementation of Python such as CPython, Jython, or IronPython. If either option is used with Python 2.6, the interpreter will report that the option isn’t currently used.</p> <p>Python can now be prevented from writing <code class="file docutils literal notranslate"><span class="pre">.pyc</span></code> or <code class="file docutils literal notranslate"><span class="pre">.pyo</span></code> files by supplying the <a class="reference internal" href="../using/cmdline.html#id1"><code class="xref std std-option docutils literal notranslate"><span class="pre">-B</span></code></a> switch to the Python interpreter, or by setting the <span class="target" id="index-20"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONDONTWRITEBYTECODE"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONDONTWRITEBYTECODE</span></code></a> environment variable before running the interpreter. This setting is available to Python programs as the <code class="docutils literal notranslate"><span class="pre">sys.dont_write_bytecode</span></code> variable, and Python code can change the value to modify the interpreter’s behaviour. (Contributed by Neal Norwitz and Georg Brandl.)</p> <p>The encoding used for standard input, output, and standard error can be specified by setting the <span class="target" id="index-21"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONIOENCODING"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONIOENCODING</span></code></a> environment variable before running the interpreter. The value should be a string in the form <code class="docutils literal notranslate"><span class="pre"><encoding></span></code> or <code class="docutils literal notranslate"><span class="pre"><encoding>:<errorhandler></span></code>. The <em>encoding</em> part specifies the encoding’s name, e.g. <code class="docutils literal notranslate"><span class="pre">utf-8</span></code> or <code class="docutils literal notranslate"><span class="pre">latin-1</span></code>; the optional <em>errorhandler</em> part specifies what to do with characters that can’t be handled by the encoding, and should be one of “error”, “ignore”, or “replace”. (Contributed by Martin von Löwis.)</p> </div> </div> <div class="section" id="new-and-improved-modules"> <h2>New and Improved Modules<a class="headerlink" href="#new-and-improved-modules" title="Permalink to this headline">¶</a></h2> <p>As in every release, Python’s standard library received a number of enhancements and bug fixes. Here’s a partial list of the most notable changes, sorted alphabetically by module name. Consult the <code class="file docutils literal notranslate"><span class="pre">Misc/NEWS</span></code> file in the source tree for a more complete list of changes, or look through the Subversion logs for all the details.</p> <ul> <li><p class="first">The <a class="reference internal" href="../library/asyncore.html#module-asyncore" title="asyncore: A base class for developing asynchronous socket handling services."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncore</span></code></a> and <a class="reference internal" href="../library/asynchat.html#module-asynchat" title="asynchat: Support for asynchronous command/response protocols."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asynchat</span></code></a> modules are being actively maintained again, and a number of patches and bugfixes were applied. (Maintained by Josiah Carlson; see <a class="reference external" href="https://bugs.python.org/issue1736190">bpo-1736190</a> for one patch.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">bsddb</span></code> module also has a new maintainer, Jesús Cea Avión, and the package is now available as a standalone package. The web page for the package is <a class="reference external" href="https://www.jcea.es/programacion/pybsddb.htm">www.jcea.es/programacion/pybsddb.htm</a>. The plan is to remove the package from the standard library in Python 3.0, because its pace of releases is much more frequent than Python’s.</p> <p>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">bsddb.dbshelve</span></code> module now uses the highest pickling protocol available, instead of restricting itself to protocol 1. (Contributed by W. Barnes.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/cgi.html#module-cgi" title="cgi: Helpers for running Python scripts via the Common Gateway Interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cgi</span></code></a> module will now read variables from the query string of an HTTP POST request. This makes it possible to use form actions with URLs that include query strings such as “/cgi-bin/add.py?category=1”. (Contributed by Alexandre Fiori and Nubis; <a class="reference external" href="https://bugs.python.org/issue1817">bpo-1817</a>.)</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">parse_qs()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">parse_qsl()</span></code> functions have been relocated from the <a class="reference internal" href="../library/cgi.html#module-cgi" title="cgi: Helpers for running Python scripts via the Common Gateway Interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cgi</span></code></a> module to the <code class="xref py py-mod docutils literal notranslate"><span class="pre">urlparse</span></code> module. The versions still available in the <a class="reference internal" href="../library/cgi.html#module-cgi" title="cgi: Helpers for running Python scripts via the Common Gateway Interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cgi</span></code></a> module will trigger <a class="reference internal" href="../library/exceptions.html#PendingDeprecationWarning" title="PendingDeprecationWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">PendingDeprecationWarning</span></code></a> messages in 2.6 (<a class="reference external" href="https://bugs.python.org/issue600362">bpo-600362</a>).</p> </li> <li><p class="first">The <a class="reference internal" href="../library/cmath.html#module-cmath" title="cmath: Mathematical functions for complex numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cmath</span></code></a> module underwent extensive revision, contributed by Mark Dickinson and Christian Heimes. Five new functions were added:</p> <ul class="simple"> <li><code class="xref py py-func docutils literal notranslate"><span class="pre">polar()</span></code> converts a complex number to polar form, returning the modulus and argument of the complex number.</li> <li><code class="xref py py-func docutils literal notranslate"><span class="pre">rect()</span></code> does the opposite, turning a modulus, argument pair back into the corresponding complex number.</li> <li><code class="xref py py-func docutils literal notranslate"><span class="pre">phase()</span></code> returns the argument (also called the angle) of a complex number.</li> <li><code class="xref py py-func docutils literal notranslate"><span class="pre">isnan()</span></code> returns True if either the real or imaginary part of its argument is a NaN.</li> <li><code class="xref py py-func docutils literal notranslate"><span class="pre">isinf()</span></code> returns True if either the real or imaginary part of its argument is infinite.</li> </ul> <p>The revisions also improved the numerical soundness of the <a class="reference internal" href="../library/cmath.html#module-cmath" title="cmath: Mathematical functions for complex numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cmath</span></code></a> module. For all functions, the real and imaginary parts of the results are accurate to within a few units of least precision (ulps) whenever possible. See <a class="reference external" href="https://bugs.python.org/issue1381">bpo-1381</a> for the details. The branch cuts for <code class="xref py py-func docutils literal notranslate"><span class="pre">asinh()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">atanh()</span></code>: and <code class="xref py py-func docutils literal notranslate"><span class="pre">atan()</span></code> have also been corrected.</p> <p>The tests for the module have been greatly expanded; nearly 2000 new test cases exercise the algebraic functions.</p> <p>On IEEE 754 platforms, the <a class="reference internal" href="../library/cmath.html#module-cmath" title="cmath: Mathematical functions for complex numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cmath</span></code></a> module now handles IEEE 754 special values and floating-point exceptions in a manner consistent with Annex ‘G’ of the C99 standard.</p> </li> <li><p class="first">A new data type in the <a class="reference internal" href="../library/collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate"><span class="pre">collections</span></code></a> module: <code class="xref py py-class docutils literal notranslate"><span class="pre">namedtuple(typename,</span> <span class="pre">fieldnames)</span></code> is a factory function that creates subclasses of the standard tuple whose fields are accessible by name as well as index. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">var_type</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">namedtuple</span><span class="p">(</span><span class="s1">'variable'</span><span class="p">,</span> <span class="gp">... </span> <span class="s1">'id name type size'</span><span class="p">)</span> <span class="gp">>>> </span><span class="c1"># Names are separated by spaces or commas.</span> <span class="gp">>>> </span><span class="c1"># 'id, name, type, size' would also work.</span> <span class="gp">>>> </span><span class="n">var_type</span><span class="o">.</span><span class="n">_fields</span> <span class="go">('id', 'name', 'type', 'size')</span> <span class="gp">>>> </span><span class="n">var</span> <span class="o">=</span> <span class="n">var_type</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="s1">'frequency'</span><span class="p">,</span> <span class="s1">'int'</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">var</span><span class="p">[</span><span class="mi">0</span><span class="p">],</span> <span class="n">var</span><span class="o">.</span><span class="n">id</span> <span class="c1"># Equivalent</span> <span class="go">1 1</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">var</span><span class="p">[</span><span class="mi">2</span><span class="p">],</span> <span class="n">var</span><span class="o">.</span><span class="n">type</span> <span class="c1"># Equivalent</span> <span class="go">int int</span> <span class="gp">>>> </span><span class="n">var</span><span class="o">.</span><span class="n">_asdict</span><span class="p">()</span> <span class="go">{'size': 4, 'type': 'int', 'id': 1, 'name': 'frequency'}</span> <span class="gp">>>> </span><span class="n">v2</span> <span class="o">=</span> <span class="n">var</span><span class="o">.</span><span class="n">_replace</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">'amplitude'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">v2</span> <span class="go">variable(id=1, name='amplitude', type='int', size=4)</span> </pre></div> </div> <p>Several places in the standard library that returned tuples have been modified to return <code class="xref py py-class docutils literal notranslate"><span class="pre">namedtuple</span></code> instances. For example, the <code class="xref py py-meth docutils literal notranslate"><span class="pre">Decimal.as_tuple()</span></code> method now returns a named tuple with <code class="xref py py-attr docutils literal notranslate"><span class="pre">sign</span></code>, <code class="xref py py-attr docutils literal notranslate"><span class="pre">digits</span></code>, and <code class="xref py py-attr docutils literal notranslate"><span class="pre">exponent</span></code> fields.</p> <p>(Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">Another change to the <a class="reference internal" href="../library/collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate"><span class="pre">collections</span></code></a> module is that the <code class="xref py py-class docutils literal notranslate"><span class="pre">deque</span></code> type now supports an optional <em>maxlen</em> parameter; if supplied, the deque’s size will be restricted to no more than <em>maxlen</em> items. Adding more items to a full deque causes old items to be discarded.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">collections</span> <span class="k">import</span> <span class="n">deque</span> <span class="gp">>>> </span><span class="n">dq</span><span class="o">=</span><span class="n">deque</span><span class="p">(</span><span class="n">maxlen</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">dq</span> <span class="go">deque([], maxlen=3)</span> <span class="gp">>>> </span><span class="n">dq</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span> <span class="n">dq</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">2</span><span class="p">);</span> <span class="n">dq</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">dq</span> <span class="go">deque([1, 2, 3], maxlen=3)</span> <span class="gp">>>> </span><span class="n">dq</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">dq</span> <span class="go">deque([2, 3, 4], maxlen=3)</span> </pre></div> </div> <p>(Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">Cookie</span></code> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">Morsel</span></code> objects now support an <code class="xref py py-attr docutils literal notranslate"><span class="pre">httponly</span></code> attribute. In some browsers. cookies with this attribute set cannot be accessed or manipulated by JavaScript code. (Contributed by Arvin Schnell; <a class="reference external" href="https://bugs.python.org/issue1638033">bpo-1638033</a>.)</p> </li> <li><p class="first">A new window method in the <a class="reference internal" href="../library/curses.html#module-curses" title="curses: An interface to the curses library, providing portable terminal handling. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses</span></code></a> module, <code class="xref py py-meth docutils literal notranslate"><span class="pre">chgat()</span></code>, changes the display attributes for a certain number of characters on a single line. (Contributed by Fabian Kreutz.)</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># Boldface text starting at y=0,x=21</span> <span class="c1"># and affecting the rest of the line.</span> <span class="n">stdscr</span><span class="o">.</span><span class="n">chgat</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">21</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">A_BOLD</span><span class="p">)</span> </pre></div> </div> <p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">Textbox</span></code> class in the <a class="reference internal" href="../library/curses.html#module-curses.textpad" title="curses.textpad: Emacs-like input editing in a curses window."><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses.textpad</span></code></a> module now supports editing in insert mode as well as overwrite mode. Insert mode is enabled by supplying a true value for the <em>insert_mode</em> parameter when creating the <code class="xref py py-class docutils literal notranslate"><span class="pre">Textbox</span></code> instance.</p> </li> <li><p class="first">The <a class="reference internal" href="../library/datetime.html#module-datetime" title="datetime: Basic date and time types."><code class="xref py py-mod docutils literal notranslate"><span class="pre">datetime</span></code></a> module’s <code class="xref py py-meth docutils literal notranslate"><span class="pre">strftime()</span></code> methods now support a <code class="docutils literal notranslate"><span class="pre">%f</span></code> format code that expands to the number of microseconds in the object, zero-padded on the left to six places. (Contributed by Skip Montanaro; <a class="reference external" href="https://bugs.python.org/issue1158">bpo-1158</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/decimal.html#module-decimal" title="decimal: Implementation of the General Decimal Arithmetic Specification."><code class="xref py py-mod docutils literal notranslate"><span class="pre">decimal</span></code></a> module was updated to version 1.66 of <a class="reference external" href="http://speleotrove.com/decimal/decarith.html">the General Decimal Specification</a>. New features include some methods for some basic mathematical functions such as <code class="xref py py-meth docutils literal notranslate"><span class="pre">exp()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">log10()</span></code>:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Decimal</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">.</span><span class="n">exp</span><span class="p">()</span> <span class="go">Decimal("2.718281828459045235360287471")</span> <span class="gp">>>> </span><span class="n">Decimal</span><span class="p">(</span><span class="s2">"2.7182818"</span><span class="p">)</span><span class="o">.</span><span class="n">ln</span><span class="p">()</span> <span class="go">Decimal("0.9999999895305022877376682436")</span> <span class="gp">>>> </span><span class="n">Decimal</span><span class="p">(</span><span class="mi">1000</span><span class="p">)</span><span class="o">.</span><span class="n">log10</span><span class="p">()</span> <span class="go">Decimal("3")</span> </pre></div> </div> <p>The <code class="xref py py-meth docutils literal notranslate"><span class="pre">as_tuple()</span></code> method of <code class="xref py py-class docutils literal notranslate"><span class="pre">Decimal</span></code> objects now returns a named tuple with <code class="xref py py-attr docutils literal notranslate"><span class="pre">sign</span></code>, <code class="xref py py-attr docutils literal notranslate"><span class="pre">digits</span></code>, and <code class="xref py py-attr docutils literal notranslate"><span class="pre">exponent</span></code> fields.</p> <p>(Implemented by Facundo Batista and Mark Dickinson. Named tuple support added by Raymond Hettinger.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/difflib.html#module-difflib" title="difflib: Helpers for computing differences between objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">difflib</span></code></a> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">SequenceMatcher</span></code> class now returns named tuples representing matches, with <code class="xref py py-attr docutils literal notranslate"><span class="pre">a</span></code>, <code class="xref py py-attr docutils literal notranslate"><span class="pre">b</span></code>, and <code class="xref py py-attr docutils literal notranslate"><span class="pre">size</span></code> attributes. (Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">An optional <code class="docutils literal notranslate"><span class="pre">timeout</span></code> parameter, specifying a timeout measured in seconds, was added to the <a class="reference internal" href="../library/ftplib.html#ftplib.FTP" title="ftplib.FTP"><code class="xref py py-class docutils literal notranslate"><span class="pre">ftplib.FTP</span></code></a> class constructor as well as the <code class="xref py py-meth docutils literal notranslate"><span class="pre">connect()</span></code> method. (Added by Facundo Batista.) Also, the <code class="xref py py-class docutils literal notranslate"><span class="pre">FTP</span></code> class’s <code class="xref py py-meth docutils literal notranslate"><span class="pre">storbinary()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">storlines()</span></code> now take an optional <em>callback</em> parameter that will be called with each block of data after the data has been sent. (Contributed by Phil Schwartz; <a class="reference external" href="https://bugs.python.org/issue1221598">bpo-1221598</a>.)</p> </li> <li><p class="first">The <code class="xref py py-func docutils literal notranslate"><span class="pre">reduce()</span></code> built-in function is also available in the <a class="reference internal" href="../library/functools.html#module-functools" title="functools: Higher-order functions and operations on callable objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">functools</span></code></a> module. In Python 3.0, the builtin has been dropped and <code class="xref py py-func docutils literal notranslate"><span class="pre">reduce()</span></code> is only available from <a class="reference internal" href="../library/functools.html#module-functools" title="functools: Higher-order functions and operations on callable objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">functools</span></code></a>; currently there are no plans to drop the builtin in the 2.x series. (Patched by Christian Heimes; <a class="reference external" href="https://bugs.python.org/issue1739906">bpo-1739906</a>.)</p> </li> <li><p class="first">When possible, the <a class="reference internal" href="../library/getpass.html#module-getpass" title="getpass: Portable reading of passwords and retrieval of the userid."><code class="xref py py-mod docutils literal notranslate"><span class="pre">getpass</span></code></a> module will now use <code class="file docutils literal notranslate"><span class="pre">/dev/tty</span></code> to print a prompt message and read the password, falling back to standard error and standard input. If the password may be echoed to the terminal, a warning is printed before the prompt is displayed. (Contributed by Gregory P. Smith.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/glob.html#glob.glob" title="glob.glob"><code class="xref py py-func docutils literal notranslate"><span class="pre">glob.glob()</span></code></a> function can now return Unicode filenames if a Unicode path was used and Unicode filenames are matched within the directory. (<a class="reference external" href="https://bugs.python.org/issue1001604">bpo-1001604</a>)</p> </li> <li><p class="first">A new function in the <a class="reference internal" href="../library/heapq.html#module-heapq" title="heapq: Heap queue algorithm (a.k.a. priority queue)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">heapq</span></code></a> module, <code class="docutils literal notranslate"><span class="pre">merge(iter1,</span> <span class="pre">iter2,</span> <span class="pre">...)</span></code>, takes any number of iterables returning data in sorted order, and returns a new generator that returns the contents of all the iterators, also in sorted order. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">heapq</span><span class="o">.</span><span class="n">merge</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">9</span><span class="p">],</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">16</span><span class="p">]))</span> <span class="go">[1, 2, 3, 5, 8, 9, 16]</span> </pre></div> </div> <p>Another new function, <code class="docutils literal notranslate"><span class="pre">heappushpop(heap,</span> <span class="pre">item)</span></code>, pushes <em>item</em> onto <em>heap</em>, then pops off and returns the smallest item. This is more efficient than making a call to <code class="xref py py-func docutils literal notranslate"><span class="pre">heappush()</span></code> and then <code class="xref py py-func docutils literal notranslate"><span class="pre">heappop()</span></code>.</p> <p><a class="reference internal" href="../library/heapq.html#module-heapq" title="heapq: Heap queue algorithm (a.k.a. priority queue)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">heapq</span></code></a> is now implemented to only use less-than comparison, instead of the less-than-or-equal comparison it previously used. This makes <a class="reference internal" href="../library/heapq.html#module-heapq" title="heapq: Heap queue algorithm (a.k.a. priority queue)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">heapq</span></code></a>’s usage of a type match the <a class="reference internal" href="../library/stdtypes.html#list.sort" title="list.sort"><code class="xref py py-meth docutils literal notranslate"><span class="pre">list.sort()</span></code></a> method. (Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">An optional <code class="docutils literal notranslate"><span class="pre">timeout</span></code> parameter, specifying a timeout measured in seconds, was added to the <code class="xref py py-class docutils literal notranslate"><span class="pre">httplib.HTTPConnection</span></code> and <code class="xref py py-class docutils literal notranslate"><span class="pre">HTTPSConnection</span></code> class constructors. (Added by Facundo Batista.)</p> </li> <li><p class="first">Most of the <a class="reference internal" href="../library/inspect.html#module-inspect" title="inspect: Extract information and source code from live objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">inspect</span></code></a> module’s functions, such as <code class="xref py py-func docutils literal notranslate"><span class="pre">getmoduleinfo()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">getargs()</span></code>, now return named tuples. In addition to behaving like tuples, the elements of the return value can also be accessed as attributes. (Contributed by Raymond Hettinger.)</p> <p>Some new functions in the module include <code class="xref py py-func docutils literal notranslate"><span class="pre">isgenerator()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">isgeneratorfunction()</span></code>, and <code class="xref py py-func docutils literal notranslate"><span class="pre">isabstract()</span></code>.</p> </li> <li><p class="first">The <a class="reference internal" href="../library/itertools.html#module-itertools" title="itertools: Functions creating iterators for efficient looping."><code class="xref py py-mod docutils literal notranslate"><span class="pre">itertools</span></code></a> module gained several new functions.</p> <p><code class="docutils literal notranslate"><span class="pre">izip_longest(iter1,</span> <span class="pre">iter2,</span> <span class="pre">...[,</span> <span class="pre">fillvalue])</span></code> makes tuples from each of the elements; if some of the iterables are shorter than others, the missing values are set to <em>fillvalue</em>. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">tuple</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">izip_longest</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">]))</span> <span class="go">((1, 1), (2, 2), (3, 3), (None, 4), (None, 5))</span> </pre></div> </div> <p><code class="docutils literal notranslate"><span class="pre">product(iter1,</span> <span class="pre">iter2,</span> <span class="pre">...,</span> <span class="pre">[repeat=N])</span></code> returns the Cartesian product of the supplied iterables, a set of tuples containing every possible combination of the elements returned from each iterable.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">product</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">]))</span> <span class="go">[(1, 4), (1, 5), (1, 6),</span> <span class="go"> (2, 4), (2, 5), (2, 6),</span> <span class="go"> (3, 4), (3, 5), (3, 6)]</span> </pre></div> </div> <p>The optional <em>repeat</em> keyword argument is used for taking the product of an iterable or a set of iterables with themselves, repeated <em>N</em> times. With a single iterable argument, <em>N</em>-tuples are returned:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">product</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">],</span> <span class="n">repeat</span><span class="o">=</span><span class="mi">3</span><span class="p">))</span> <span class="go">[(1, 1, 1), (1, 1, 2), (1, 2, 1), (1, 2, 2),</span> <span class="go"> (2, 1, 1), (2, 1, 2), (2, 2, 1), (2, 2, 2)]</span> </pre></div> </div> <p>With two iterables, <em>2N</em>-tuples are returned.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">product</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">],</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">],</span> <span class="n">repeat</span><span class="o">=</span><span class="mi">2</span><span class="p">))</span> <span class="go">[(1, 3, 1, 3), (1, 3, 1, 4), (1, 3, 2, 3), (1, 3, 2, 4),</span> <span class="go"> (1, 4, 1, 3), (1, 4, 1, 4), (1, 4, 2, 3), (1, 4, 2, 4),</span> <span class="go"> (2, 3, 1, 3), (2, 3, 1, 4), (2, 3, 2, 3), (2, 3, 2, 4),</span> <span class="go"> (2, 4, 1, 3), (2, 4, 1, 4), (2, 4, 2, 3), (2, 4, 2, 4)]</span> </pre></div> </div> <p><code class="docutils literal notranslate"><span class="pre">combinations(iterable,</span> <span class="pre">r)</span></code> returns sub-sequences of length <em>r</em> from the elements of <em>iterable</em>.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">combinations</span><span class="p">(</span><span class="s1">'123'</span><span class="p">,</span> <span class="mi">2</span><span class="p">))</span> <span class="go">[('1', '2'), ('1', '3'), ('2', '3')]</span> <span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">combinations</span><span class="p">(</span><span class="s1">'123'</span><span class="p">,</span> <span class="mi">3</span><span class="p">))</span> <span class="go">[('1', '2', '3')]</span> <span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">combinations</span><span class="p">(</span><span class="s1">'1234'</span><span class="p">,</span> <span class="mi">3</span><span class="p">))</span> <span class="go">[('1', '2', '3'), ('1', '2', '4'),</span> <span class="go"> ('1', '3', '4'), ('2', '3', '4')]</span> </pre></div> </div> <p><code class="docutils literal notranslate"><span class="pre">permutations(iter[,</span> <span class="pre">r])</span></code> returns all the permutations of length <em>r</em> of the iterable’s elements. If <em>r</em> is not specified, it will default to the number of elements produced by the iterable.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">permutations</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">],</span> <span class="mi">2</span><span class="p">))</span> <span class="go">[(1, 2), (1, 3), (1, 4),</span> <span class="go"> (2, 1), (2, 3), (2, 4),</span> <span class="go"> (3, 1), (3, 2), (3, 4),</span> <span class="go"> (4, 1), (4, 2), (4, 3)]</span> </pre></div> </div> <p><code class="docutils literal notranslate"><span class="pre">itertools.chain(*iterables)</span></code> is an existing function in <a class="reference internal" href="../library/itertools.html#module-itertools" title="itertools: Functions creating iterators for efficient looping."><code class="xref py py-mod docutils literal notranslate"><span class="pre">itertools</span></code></a> that gained a new constructor in Python 2.6. <code class="docutils literal notranslate"><span class="pre">itertools.chain.from_iterable(iterable)</span></code> takes a single iterable that should return other iterables. <code class="xref py py-func docutils literal notranslate"><span class="pre">chain()</span></code> will then return all the elements of the first iterable, then all the elements of the second, and so on.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">itertools</span><span class="o">.</span><span class="n">chain</span><span class="o">.</span><span class="n">from_iterable</span><span class="p">([[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">]]))</span> <span class="go">[1, 2, 3, 4, 5, 6]</span> </pre></div> </div> <p>(All contributed by Raymond Hettinger.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate"><span class="pre">logging</span></code></a> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">FileHandler</span></code> class and its subclasses <code class="xref py py-class docutils literal notranslate"><span class="pre">WatchedFileHandler</span></code>, <code class="xref py py-class docutils literal notranslate"><span class="pre">RotatingFileHandler</span></code>, and <code class="xref py py-class docutils literal notranslate"><span class="pre">TimedRotatingFileHandler</span></code> now have an optional <em>delay</em> parameter to their constructors. If <em>delay</em> is true, opening of the log file is deferred until the first <code class="xref py py-meth docutils literal notranslate"><span class="pre">emit()</span></code> call is made. (Contributed by Vinay Sajip.)</p> <p><code class="xref py py-class docutils literal notranslate"><span class="pre">TimedRotatingFileHandler</span></code> also has a <em>utc</em> constructor parameter. If the argument is true, UTC time will be used in determining when midnight occurs and in generating filenames; otherwise local time will be used.</p> </li> <li><p class="first">Several new functions were added to the <a class="reference internal" href="../library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">math</span></code></a> module:</p> <ul class="simple"> <li><a class="reference internal" href="../library/math.html#math.isinf" title="math.isinf"><code class="xref py py-func docutils literal notranslate"><span class="pre">isinf()</span></code></a> and <a class="reference internal" href="../library/math.html#math.isnan" title="math.isnan"><code class="xref py py-func docutils literal notranslate"><span class="pre">isnan()</span></code></a> determine whether a given float is a (positive or negative) infinity or a NaN (Not a Number), respectively.</li> <li><a class="reference internal" href="../library/math.html#math.copysign" title="math.copysign"><code class="xref py py-func docutils literal notranslate"><span class="pre">copysign()</span></code></a> copies the sign bit of an IEEE 754 number, returning the absolute value of <em>x</em> combined with the sign bit of <em>y</em>. For example, <code class="docutils literal notranslate"><span class="pre">math.copysign(1,</span> <span class="pre">-0.0)</span></code> returns -1.0. (Contributed by Christian Heimes.)</li> <li><a class="reference internal" href="../library/math.html#math.factorial" title="math.factorial"><code class="xref py py-func docutils literal notranslate"><span class="pre">factorial()</span></code></a> computes the factorial of a number. (Contributed by Raymond Hettinger; <a class="reference external" href="https://bugs.python.org/issue2138">bpo-2138</a>.)</li> <li><a class="reference internal" href="../library/math.html#math.fsum" title="math.fsum"><code class="xref py py-func docutils literal notranslate"><span class="pre">fsum()</span></code></a> adds up the stream of numbers from an iterable, and is careful to avoid loss of precision through using partial sums. (Contributed by Jean Brouwers, Raymond Hettinger, and Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue2819">bpo-2819</a>.)</li> <li><a class="reference internal" href="../library/math.html#math.acosh" title="math.acosh"><code class="xref py py-func docutils literal notranslate"><span class="pre">acosh()</span></code></a>, <a class="reference internal" href="../library/math.html#math.asinh" title="math.asinh"><code class="xref py py-func docutils literal notranslate"><span class="pre">asinh()</span></code></a> and <a class="reference internal" href="../library/math.html#math.atanh" title="math.atanh"><code class="xref py py-func docutils literal notranslate"><span class="pre">atanh()</span></code></a> compute the inverse hyperbolic functions.</li> <li><a class="reference internal" href="../library/math.html#math.log1p" title="math.log1p"><code class="xref py py-func docutils literal notranslate"><span class="pre">log1p()</span></code></a> returns the natural logarithm of <em>1+x</em> (base <em>e</em>).</li> <li><code class="xref py py-func docutils literal notranslate"><span class="pre">trunc()</span></code> rounds a number toward zero, returning the closest <code class="xref py py-class docutils literal notranslate"><span class="pre">Integral</span></code> that’s between the function’s argument and zero. Added as part of the backport of <a class="reference external" href="#pep-3141">PEP 3141’s type hierarchy for numbers</a>.</li> </ul> </li> <li><p class="first">The <a class="reference internal" href="../library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">math</span></code></a> module has been improved to give more consistent behaviour across platforms, especially with respect to handling of floating-point exceptions and IEEE 754 special values.</p> <p>Whenever possible, the module follows the recommendations of the C99 standard about 754’s special values. For example, <code class="docutils literal notranslate"><span class="pre">sqrt(-1.)</span></code> should now give a <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> across almost all platforms, while <code class="docutils literal notranslate"><span class="pre">sqrt(float('NaN'))</span></code> should return a NaN on all IEEE 754 platforms. Where Annex ‘F’ of the C99 standard recommends signaling ‘divide-by-zero’ or ‘invalid’, Python will raise <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>. Where Annex ‘F’ of the C99 standard recommends signaling ‘overflow’, Python will raise <a class="reference internal" href="../library/exceptions.html#OverflowError" title="OverflowError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OverflowError</span></code></a>. (See <a class="reference external" href="https://bugs.python.org/issue711019">bpo-711019</a> and <a class="reference external" href="https://bugs.python.org/issue1640">bpo-1640</a>.)</p> <p>(Contributed by Christian Heimes and Mark Dickinson.)</p> </li> <li><p class="first"><a class="reference internal" href="../library/mmap.html#mmap.mmap" title="mmap.mmap"><code class="xref py py-class docutils literal notranslate"><span class="pre">mmap</span></code></a> objects now have a <code class="xref py py-meth docutils literal notranslate"><span class="pre">rfind()</span></code> method that searches for a substring beginning at the end of the string and searching backwards. The <code class="xref py py-meth docutils literal notranslate"><span class="pre">find()</span></code> method also gained an <em>end</em> parameter giving an index at which to stop searching. (Contributed by John Lenton.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/operator.html#module-operator" title="operator: Functions corresponding to the standard operators."><code class="xref py py-mod docutils literal notranslate"><span class="pre">operator</span></code></a> module gained a <code class="xref py py-func docutils literal notranslate"><span class="pre">methodcaller()</span></code> function that takes a name and an optional set of arguments, returning a callable that will call the named function on any arguments passed to it. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="c1"># Equivalent to lambda s: s.replace('old', 'new')</span> <span class="gp">>>> </span><span class="n">replacer</span> <span class="o">=</span> <span class="n">operator</span><span class="o">.</span><span class="n">methodcaller</span><span class="p">(</span><span class="s1">'replace'</span><span class="p">,</span> <span class="s1">'old'</span><span class="p">,</span> <span class="s1">'new'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">replacer</span><span class="p">(</span><span class="s1">'old wine in old bottles'</span><span class="p">)</span> <span class="go">'new wine in new bottles'</span> </pre></div> </div> <p>(Contributed by Georg Brandl, after a suggestion by Gregory Petrosyan.)</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">attrgetter()</span></code> function now accepts dotted names and performs the corresponding attribute lookups:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">inst_name</span> <span class="o">=</span> <span class="n">operator</span><span class="o">.</span><span class="n">attrgetter</span><span class="p">(</span> <span class="gp">... </span> <span class="s1">'__class__.__name__'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">inst_name</span><span class="p">(</span><span class="s1">''</span><span class="p">)</span> <span class="go">'str'</span> <span class="gp">>>> </span><span class="n">inst_name</span><span class="p">(</span><span class="n">help</span><span class="p">)</span> <span class="go">'_Helper'</span> </pre></div> </div> <p>(Contributed by Georg Brandl, after a suggestion by Barry Warsaw.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module now wraps several new system calls. <code class="docutils literal notranslate"><span class="pre">fchmod(fd,</span> <span class="pre">mode)</span></code> and <code class="docutils literal notranslate"><span class="pre">fchown(fd,</span> <span class="pre">uid,</span> <span class="pre">gid)</span></code> change the mode and ownership of an opened file, and <code class="docutils literal notranslate"><span class="pre">lchmod(path,</span> <span class="pre">mode)</span></code> changes the mode of a symlink. (Contributed by Georg Brandl and Christian Heimes.)</p> <p><code class="xref py py-func docutils literal notranslate"><span class="pre">chflags()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">lchflags()</span></code> are wrappers for the corresponding system calls (where they’re available), changing the flags set on a file. Constants for the flag values are defined in the <a class="reference internal" href="../library/stat.html#module-stat" title="stat: Utilities for interpreting the results of os.stat(), os.lstat() and os.fstat()."><code class="xref py py-mod docutils literal notranslate"><span class="pre">stat</span></code></a> module; some possible values include <code class="xref py py-const docutils literal notranslate"><span class="pre">UF_IMMUTABLE</span></code> to signal the file may not be changed and <code class="xref py py-const docutils literal notranslate"><span class="pre">UF_APPEND</span></code> to indicate that data can only be appended to the file. (Contributed by M. Levinson.)</p> <p><code class="docutils literal notranslate"><span class="pre">os.closerange(low,</span> <span class="pre">high)</span></code> efficiently closes all file descriptors from <em>low</em> to <em>high</em>, ignoring any errors and not including <em>high</em> itself. This function is now used by the <a class="reference internal" href="../library/subprocess.html#module-subprocess" title="subprocess: Subprocess management."><code class="xref py py-mod docutils literal notranslate"><span class="pre">subprocess</span></code></a> module to make starting processes faster. (Contributed by Georg Brandl; <a class="reference external" href="https://bugs.python.org/issue1663329">bpo-1663329</a>.)</p> </li> <li><p class="first">The <code class="docutils literal notranslate"><span class="pre">os.environ</span></code> object’s <code class="xref py py-meth docutils literal notranslate"><span class="pre">clear()</span></code> method will now unset the environment variables using <a class="reference internal" href="../library/os.html#os.unsetenv" title="os.unsetenv"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.unsetenv()</span></code></a> in addition to clearing the object’s keys. (Contributed by Martin Horcicka; <a class="reference external" href="https://bugs.python.org/issue1181">bpo-1181</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/os.html#os.walk" title="os.walk"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.walk()</span></code></a> function now has a <code class="docutils literal notranslate"><span class="pre">followlinks</span></code> parameter. If set to True, it will follow symlinks pointing to directories and visit the directory’s contents. For backward compatibility, the parameter’s default value is false. Note that the function can fall into an infinite recursion if there’s a symlink that points to a parent directory. (<a class="reference external" href="https://bugs.python.org/issue1273829">bpo-1273829</a>)</p> </li> <li><p class="first">In the <a class="reference internal" href="../library/os.path.html#module-os.path" title="os.path: Operations on pathnames."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os.path</span></code></a> module, the <code class="xref py py-func docutils literal notranslate"><span class="pre">splitext()</span></code> function has been changed to not split on leading period characters. This produces better results when operating on Unix’s dot-files. For example, <code class="docutils literal notranslate"><span class="pre">os.path.splitext('.ipython')</span></code> now returns <code class="docutils literal notranslate"><span class="pre">('.ipython',</span> <span class="pre">'')</span></code> instead of <code class="docutils literal notranslate"><span class="pre">('',</span> <span class="pre">'.ipython')</span></code>. (<a class="reference external" href="https://bugs.python.org/issue1115886">bpo-1115886</a>)</p> <p>A new function, <code class="docutils literal notranslate"><span class="pre">os.path.relpath(path,</span> <span class="pre">start='.')</span></code>, returns a relative path from the <code class="docutils literal notranslate"><span class="pre">start</span></code> path, if it’s supplied, or from the current working directory to the destination <code class="docutils literal notranslate"><span class="pre">path</span></code>. (Contributed by Richard Barran; <a class="reference external" href="https://bugs.python.org/issue1339796">bpo-1339796</a>.)</p> <p>On Windows, <a class="reference internal" href="../library/os.path.html#os.path.expandvars" title="os.path.expandvars"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.path.expandvars()</span></code></a> will now expand environment variables given in the form “%var%”, and “~user” will be expanded into the user’s home directory path. (Contributed by Josiah Carlson; <a class="reference external" href="https://bugs.python.org/issue957650">bpo-957650</a>.)</p> </li> <li><p class="first">The Python debugger provided by the <a class="reference internal" href="../library/pdb.html#module-pdb" title="pdb: The Python debugger for interactive interpreters."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pdb</span></code></a> module gained a new command: “run” restarts the Python program being debugged and can optionally take new command-line arguments for the program. (Contributed by Rocky Bernstein; <a class="reference external" href="https://bugs.python.org/issue1393667">bpo-1393667</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/pdb.html#pdb.post_mortem" title="pdb.post_mortem"><code class="xref py py-func docutils literal notranslate"><span class="pre">pdb.post_mortem()</span></code></a> function, used to begin debugging a traceback, will now use the traceback returned by <a class="reference internal" href="../library/sys.html#sys.exc_info" title="sys.exc_info"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exc_info()</span></code></a> if no traceback is supplied. (Contributed by Facundo Batista; <a class="reference external" href="https://bugs.python.org/issue1106316">bpo-1106316</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/pickletools.html#module-pickletools" title="pickletools: Contains extensive comments about the pickle protocols and pickle-machine opcodes, as well as some useful functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickletools</span></code></a> module now has an <code class="xref py py-func docutils literal notranslate"><span class="pre">optimize()</span></code> function that takes a string containing a pickle and removes some unused opcodes, returning a shorter pickle that contains the same data structure. (Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">A <code class="xref py py-func docutils literal notranslate"><span class="pre">get_data()</span></code> function was added to the <a class="reference internal" href="../library/pkgutil.html#module-pkgutil" title="pkgutil: Utilities for the import system."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pkgutil</span></code></a> module that returns the contents of resource files included with an installed Python package. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">pkgutil</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">pkgutil</span><span class="o">.</span><span class="n">get_data</span><span class="p">(</span><span class="s1">'test'</span><span class="p">,</span> <span class="s1">'exception_hierarchy.txt'</span><span class="p">)</span> <span class="go">BaseException</span> <span class="go"> +-- SystemExit</span> <span class="go"> +-- KeyboardInterrupt</span> <span class="go"> +-- GeneratorExit</span> <span class="go"> +-- Exception</span> <span class="go"> +-- StopIteration</span> <span class="go"> +-- StandardError</span> <span class="go"> ...</span> </pre></div> </div> <p>(Contributed by Paul Moore; <a class="reference external" href="https://bugs.python.org/issue2439">bpo-2439</a>.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">pyexpat</span></code> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">Parser</span></code> objects now allow setting their <code class="xref py py-attr docutils literal notranslate"><span class="pre">buffer_size</span></code> attribute to change the size of the buffer used to hold character data. (Contributed by Achim Gaedke; <a class="reference external" href="https://bugs.python.org/issue1137">bpo-1137</a>.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">Queue</span></code> module now provides queue variants that retrieve entries in different orders. The <code class="xref py py-class docutils literal notranslate"><span class="pre">PriorityQueue</span></code> class stores queued items in a heap and retrieves them in priority order, and <code class="xref py py-class docutils literal notranslate"><span class="pre">LifoQueue</span></code> retrieves the most recently added entries first, meaning that it behaves like a stack. (Contributed by Raymond Hettinger.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/random.html#module-random" title="random: Generate pseudo-random numbers with various common distributions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">random</span></code></a> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">Random</span></code> objects can now be pickled on a 32-bit system and unpickled on a 64-bit system, and vice versa. Unfortunately, this change also means that Python 2.6’s <code class="xref py py-class docutils literal notranslate"><span class="pre">Random</span></code> objects can’t be unpickled correctly on earlier versions of Python. (Contributed by Shawn Ligocki; <a class="reference external" href="https://bugs.python.org/issue1727780">bpo-1727780</a>.)</p> <p>The new <code class="docutils literal notranslate"><span class="pre">triangular(low,</span> <span class="pre">high,</span> <span class="pre">mode)</span></code> function returns random numbers following a triangular distribution. The returned values are between <em>low</em> and <em>high</em>, not including <em>high</em> itself, and with <em>mode</em> as the most frequently occurring value in the distribution. (Contributed by Wladmir van der Laan and Raymond Hettinger; <a class="reference external" href="https://bugs.python.org/issue1681432">bpo-1681432</a>.)</p> </li> <li><p class="first">Long regular expression searches carried out by the <a class="reference internal" href="../library/re.html#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> module will check for signals being delivered, so time-consuming searches can now be interrupted. (Contributed by Josh Hoyt and Ralf Schmitt; <a class="reference external" href="https://bugs.python.org/issue846388">bpo-846388</a>.)</p> <p>The regular expression module is implemented by compiling bytecodes for a tiny regex-specific virtual machine. Untrusted code could create malicious strings of bytecode directly and cause crashes, so Python 2.6 includes a verifier for the regex bytecode. (Contributed by Guido van Rossum from work for Google App Engine; <a class="reference external" href="https://bugs.python.org/issue3487">bpo-3487</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/rlcompleter.html#module-rlcompleter" title="rlcompleter: Python identifier completion, suitable for the GNU readline library."><code class="xref py py-mod docutils literal notranslate"><span class="pre">rlcompleter</span></code></a> module’s <code class="xref py py-meth docutils literal notranslate"><span class="pre">Completer.complete()</span></code> method will now ignore exceptions triggered while evaluating a name. (Fixed by Lorenz Quack; <a class="reference external" href="https://bugs.python.org/issue2250">bpo-2250</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/sched.html#module-sched" title="sched: General purpose event scheduler."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sched</span></code></a> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">scheduler</span></code> instances now have a read-only <a class="reference internal" href="../library/queue.html#module-queue" title="queue: A synchronized queue class."><code class="xref py py-attr docutils literal notranslate"><span class="pre">queue</span></code></a> attribute that returns the contents of the scheduler’s queue, represented as a list of named tuples with the fields <code class="docutils literal notranslate"><span class="pre">(time,</span> <span class="pre">priority,</span> <span class="pre">action,</span> <span class="pre">argument)</span></code>. (Contributed by Raymond Hettinger; <a class="reference external" href="https://bugs.python.org/issue1861">bpo-1861</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/select.html#module-select" title="select: Wait for I/O completion on multiple streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">select</span></code></a> module now has wrapper functions for the Linux <code class="xref c c-func docutils literal notranslate"><span class="pre">epoll()</span></code> and BSD <code class="xref c c-func docutils literal notranslate"><span class="pre">kqueue()</span></code> system calls. <code class="xref py py-meth docutils literal notranslate"><span class="pre">modify()</span></code> method was added to the existing <code class="xref py py-class docutils literal notranslate"><span class="pre">poll</span></code> objects; <code class="docutils literal notranslate"><span class="pre">pollobj.modify(fd,</span> <span class="pre">eventmask)</span></code> takes a file descriptor or file object and an event mask, modifying the recorded event mask for that file. (Contributed by Christian Heimes; <a class="reference external" href="https://bugs.python.org/issue1657">bpo-1657</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/shutil.html#shutil.copytree" title="shutil.copytree"><code class="xref py py-func docutils literal notranslate"><span class="pre">shutil.copytree()</span></code></a> function now has an optional <em>ignore</em> argument that takes a callable object. This callable will receive each directory path and a list of the directory’s contents, and returns a list of names that will be ignored, not copied.</p> <p>The <a class="reference internal" href="../library/shutil.html#module-shutil" title="shutil: High-level file operations, including copying."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shutil</span></code></a> module also provides an <code class="xref py py-func docutils literal notranslate"><span class="pre">ignore_patterns()</span></code> function for use with this new parameter. <code class="xref py py-func docutils literal notranslate"><span class="pre">ignore_patterns()</span></code> takes an arbitrary number of glob-style patterns and returns a callable that will ignore any files and directories that match any of these patterns. The following example copies a directory tree, but skips both <code class="file docutils literal notranslate"><span class="pre">.svn</span></code> directories and Emacs backup files, which have names ending with ‘~’:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">shutil</span><span class="o">.</span><span class="n">copytree</span><span class="p">(</span><span class="s1">'Doc/library'</span><span class="p">,</span> <span class="s1">'/tmp/library'</span><span class="p">,</span> <span class="n">ignore</span><span class="o">=</span><span class="n">shutil</span><span class="o">.</span><span class="n">ignore_patterns</span><span class="p">(</span><span class="s1">'*~'</span><span class="p">,</span> <span class="s1">'.svn'</span><span class="p">))</span> </pre></div> </div> <p>(Contributed by Tarek Ziadé; <a class="reference external" href="https://bugs.python.org/issue2663">bpo-2663</a>.)</p> </li> <li><p class="first">Integrating signal handling with GUI handling event loops like those used by Tkinter or GTk+ has long been a problem; most software ends up polling, waking up every fraction of a second to check if any GUI events have occurred. The <a class="reference internal" href="../library/signal.html#module-signal" title="signal: Set handlers for asynchronous events."><code class="xref py py-mod docutils literal notranslate"><span class="pre">signal</span></code></a> module can now make this more efficient. Calling <code class="docutils literal notranslate"><span class="pre">signal.set_wakeup_fd(fd)</span></code> sets a file descriptor to be used; when a signal is received, a byte is written to that file descriptor. There’s also a C-level function, <a class="reference internal" href="../c-api/exceptions.html#c.PySignal_SetWakeupFd" title="PySignal_SetWakeupFd"><code class="xref c c-func docutils literal notranslate"><span class="pre">PySignal_SetWakeupFd()</span></code></a>, for setting the descriptor.</p> <p>Event loops will use this by opening a pipe to create two descriptors, one for reading and one for writing. The writable descriptor will be passed to <code class="xref py py-func docutils literal notranslate"><span class="pre">set_wakeup_fd()</span></code>, and the readable descriptor will be added to the list of descriptors monitored by the event loop via <code class="xref c c-func docutils literal notranslate"><span class="pre">select()</span></code> or <code class="xref c c-func docutils literal notranslate"><span class="pre">poll()</span></code>. On receiving a signal, a byte will be written and the main event loop will be woken up, avoiding the need to poll.</p> <p>(Contributed by Adam Olsen; <a class="reference external" href="https://bugs.python.org/issue1583">bpo-1583</a>.)</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">siginterrupt()</span></code> function is now available from Python code, and allows changing whether signals can interrupt system calls or not. (Contributed by Ralf Schmitt.)</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">setitimer()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">getitimer()</span></code> functions have also been added (where they’re available). <code class="xref py py-func docutils literal notranslate"><span class="pre">setitimer()</span></code> allows setting interval timers that will cause a signal to be delivered to the process after a specified time, measured in wall-clock time, consumed process time, or combined process+system time. (Contributed by Guilherme Polo; <a class="reference external" href="https://bugs.python.org/issue2240">bpo-2240</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/smtplib.html#module-smtplib" title="smtplib: SMTP protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">smtplib</span></code></a> module now supports SMTP over SSL thanks to the addition of the <code class="xref py py-class docutils literal notranslate"><span class="pre">SMTP_SSL</span></code> class. This class supports an interface identical to the existing <code class="xref py py-class docutils literal notranslate"><span class="pre">SMTP</span></code> class. (Contributed by Monty Taylor.) Both class constructors also have an optional <code class="docutils literal notranslate"><span class="pre">timeout</span></code> parameter that specifies a timeout for the initial connection attempt, measured in seconds. (Contributed by Facundo Batista.)</p> <p>An implementation of the LMTP protocol (<span class="target" id="index-22"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2033.html"><strong>RFC 2033</strong></a>) was also added to the module. LMTP is used in place of SMTP when transferring e-mail between agents that don’t manage a mail queue. (LMTP implemented by Leif Hedstrom; <a class="reference external" href="https://bugs.python.org/issue957003">bpo-957003</a>.)</p> <p><code class="xref py py-meth docutils literal notranslate"><span class="pre">SMTP.starttls()</span></code> now complies with <span class="target" id="index-23"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3207.html"><strong>RFC 3207</strong></a> and forgets any knowledge obtained from the server not obtained from the TLS negotiation itself. (Patch contributed by Bill Fenner; <a class="reference external" href="https://bugs.python.org/issue829951">bpo-829951</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> module now supports TIPC (<a class="reference external" href="http://tipc.sourceforge.net/">http://tipc.sourceforge.net/</a>), a high-performance non-IP-based protocol designed for use in clustered environments. TIPC addresses are 4- or 5-tuples. (Contributed by Alberto Bertogli; <a class="reference external" href="https://bugs.python.org/issue1646">bpo-1646</a>.)</p> <p>A new function, <code class="xref py py-func docutils literal notranslate"><span class="pre">create_connection()</span></code>, takes an address and connects to it using an optional timeout value, returning the connected socket object. This function also looks up the address’s type and connects to it using IPv4 or IPv6 as appropriate. Changing your code to use <code class="xref py py-func docutils literal notranslate"><span class="pre">create_connection()</span></code> instead of <code class="docutils literal notranslate"><span class="pre">socket(socket.AF_INET,</span> <span class="pre">...)</span></code> may be all that’s required to make your code work with IPv6.</p> </li> <li><p class="first">The base classes in the <code class="xref py py-mod docutils literal notranslate"><span class="pre">SocketServer</span></code> module now support calling a <code class="xref py py-meth docutils literal notranslate"><span class="pre">handle_timeout()</span></code> method after a span of inactivity specified by the server’s <code class="xref py py-attr docutils literal notranslate"><span class="pre">timeout</span></code> attribute. (Contributed by Michael Pomraning.) The <code class="xref py py-meth docutils literal notranslate"><span class="pre">serve_forever()</span></code> method now takes an optional poll interval measured in seconds, controlling how often the server will check for a shutdown request. (Contributed by Pedro Werneck and Jeffrey Yasskin; <a class="reference external" href="https://bugs.python.org/issue742598">bpo-742598</a>, <a class="reference external" href="https://bugs.python.org/issue1193577">bpo-1193577</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/sqlite3.html#module-sqlite3" title="sqlite3: A DB-API 2.0 implementation using SQLite 3.x."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sqlite3</span></code></a> module, maintained by Gerhard Häring, has been updated from version 2.3.2 in Python 2.5 to version 2.4.1.</p> </li> <li><p class="first">The <a class="reference internal" href="../library/struct.html#module-struct" title="struct: Interpret bytes as packed binary data."><code class="xref py py-mod docutils literal notranslate"><span class="pre">struct</span></code></a> module now supports the C99 <code class="xref c c-type docutils literal notranslate"><span class="pre">_Bool</span></code> type, using the format character <code class="docutils literal notranslate"><span class="pre">'?'</span></code>. (Contributed by David Remahl.)</p> </li> <li><p class="first">The <code class="xref py py-class docutils literal notranslate"><span class="pre">Popen</span></code> objects provided by the <a class="reference internal" href="../library/subprocess.html#module-subprocess" title="subprocess: Subprocess management."><code class="xref py py-mod docutils literal notranslate"><span class="pre">subprocess</span></code></a> module now have <code class="xref py py-meth docutils literal notranslate"><span class="pre">terminate()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">kill()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">send_signal()</span></code> methods. On Windows, <code class="xref py py-meth docutils literal notranslate"><span class="pre">send_signal()</span></code> only supports the <code class="xref py py-const docutils literal notranslate"><span class="pre">SIGTERM</span></code> signal, and all these methods are aliases for the Win32 API function <code class="xref c c-func docutils literal notranslate"><span class="pre">TerminateProcess()</span></code>. (Contributed by Christian Heimes.)</p> </li> <li><p class="first">A new variable in the <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a> module, <code class="xref py py-attr docutils literal notranslate"><span class="pre">float_info</span></code>, is an object containing information derived from the <code class="file docutils literal notranslate"><span class="pre">float.h</span></code> file about the platform’s floating-point support. Attributes of this object include <code class="xref py py-attr docutils literal notranslate"><span class="pre">mant_dig</span></code> (number of digits in the mantissa), <code class="xref py py-attr docutils literal notranslate"><span class="pre">epsilon</span></code> (smallest difference between 1.0 and the next largest value representable), and several others. (Contributed by Christian Heimes; <a class="reference external" href="https://bugs.python.org/issue1534">bpo-1534</a>.)</p> <p>Another new variable, <code class="xref py py-attr docutils literal notranslate"><span class="pre">dont_write_bytecode</span></code>, controls whether Python writes any <code class="file docutils literal notranslate"><span class="pre">.pyc</span></code> or <code class="file docutils literal notranslate"><span class="pre">.pyo</span></code> files on importing a module. If this variable is true, the compiled files are not written. The variable is initially set on start-up by supplying the <a class="reference internal" href="../using/cmdline.html#id1"><code class="xref std std-option docutils literal notranslate"><span class="pre">-B</span></code></a> switch to the Python interpreter, or by setting the <span class="target" id="index-24"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONDONTWRITEBYTECODE"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONDONTWRITEBYTECODE</span></code></a> environment variable before running the interpreter. Python code can subsequently change the value of this variable to control whether bytecode files are written or not. (Contributed by Neal Norwitz and Georg Brandl.)</p> <p>Information about the command-line arguments supplied to the Python interpreter is available by reading attributes of a named tuple available as <code class="docutils literal notranslate"><span class="pre">sys.flags</span></code>. For example, the <code class="xref py py-attr docutils literal notranslate"><span class="pre">verbose</span></code> attribute is true if Python was executed in verbose mode, <code class="xref py py-attr docutils literal notranslate"><span class="pre">debug</span></code> is true in debugging mode, etc. These attributes are all read-only. (Contributed by Christian Heimes.)</p> <p>A new function, <code class="xref py py-func docutils literal notranslate"><span class="pre">getsizeof()</span></code>, takes a Python object and returns the amount of memory used by the object, measured in bytes. Built-in objects return correct results; third-party extensions may not, but can define a <code class="xref py py-meth docutils literal notranslate"><span class="pre">__sizeof__()</span></code> method to return the object’s size. (Contributed by Robert Schuppenies; <a class="reference external" href="https://bugs.python.org/issue2898">bpo-2898</a>.)</p> <p>It’s now possible to determine the current profiler and tracer functions by calling <a class="reference internal" href="../library/sys.html#sys.getprofile" title="sys.getprofile"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.getprofile()</span></code></a> and <a class="reference internal" href="../library/sys.html#sys.gettrace" title="sys.gettrace"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.gettrace()</span></code></a>. (Contributed by Georg Brandl; <a class="reference external" href="https://bugs.python.org/issue1648">bpo-1648</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/tarfile.html#module-tarfile" title="tarfile: Read and write tar-format archive files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tarfile</span></code></a> module now supports POSIX.1-2001 (pax) tarfiles in addition to the POSIX.1-1988 (ustar) and GNU tar formats that were already supported. The default format is GNU tar; specify the <code class="docutils literal notranslate"><span class="pre">format</span></code> parameter to open a file using a different format:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">tar</span> <span class="o">=</span> <span class="n">tarfile</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s2">"output.tar"</span><span class="p">,</span> <span class="s2">"w"</span><span class="p">,</span> <span class="nb">format</span><span class="o">=</span><span class="n">tarfile</span><span class="o">.</span><span class="n">PAX_FORMAT</span><span class="p">)</span> </pre></div> </div> <p>The new <code class="docutils literal notranslate"><span class="pre">encoding</span></code> and <code class="docutils literal notranslate"><span class="pre">errors</span></code> parameters specify an encoding and an error handling scheme for character conversions. <code class="docutils literal notranslate"><span class="pre">'strict'</span></code>, <code class="docutils literal notranslate"><span class="pre">'ignore'</span></code>, and <code class="docutils literal notranslate"><span class="pre">'replace'</span></code> are the three standard ways Python can handle errors,; <code class="docutils literal notranslate"><span class="pre">'utf-8'</span></code> is a special value that replaces bad characters with their UTF-8 representation. (Character conversions occur because the PAX format supports Unicode filenames, defaulting to UTF-8 encoding.)</p> <p>The <code class="xref py py-meth docutils literal notranslate"><span class="pre">TarFile.add()</span></code> method now accepts an <code class="docutils literal notranslate"><span class="pre">exclude</span></code> argument that’s a function that can be used to exclude certain filenames from an archive. The function must take a filename and return true if the file should be excluded or false if it should be archived. The function is applied to both the name initially passed to <code class="xref py py-meth docutils literal notranslate"><span class="pre">add()</span></code> and to the names of files in recursively-added directories.</p> <p>(All changes contributed by Lars Gustäbel).</p> </li> <li><p class="first">An optional <code class="docutils literal notranslate"><span class="pre">timeout</span></code> parameter was added to the <a class="reference internal" href="../library/telnetlib.html#telnetlib.Telnet" title="telnetlib.Telnet"><code class="xref py py-class docutils literal notranslate"><span class="pre">telnetlib.Telnet</span></code></a> class constructor, specifying a timeout measured in seconds. (Added by Facundo Batista.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/tempfile.html#tempfile.NamedTemporaryFile" title="tempfile.NamedTemporaryFile"><code class="xref py py-class docutils literal notranslate"><span class="pre">tempfile.NamedTemporaryFile</span></code></a> class usually deletes the temporary file it created when the file is closed. This behaviour can now be changed by passing <code class="docutils literal notranslate"><span class="pre">delete=False</span></code> to the constructor. (Contributed by Damien Miller; <a class="reference external" href="https://bugs.python.org/issue1537850">bpo-1537850</a>.)</p> <p>A new class, <code class="xref py py-class docutils literal notranslate"><span class="pre">SpooledTemporaryFile</span></code>, behaves like a temporary file but stores its data in memory until a maximum size is exceeded. On reaching that limit, the contents will be written to an on-disk temporary file. (Contributed by Dustin J. Mitchell.)</p> <p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">NamedTemporaryFile</span></code> and <code class="xref py py-class docutils literal notranslate"><span class="pre">SpooledTemporaryFile</span></code> classes both work as context managers, so you can write <code class="docutils literal notranslate"><span class="pre">with</span> <span class="pre">tempfile.NamedTemporaryFile()</span> <span class="pre">as</span> <span class="pre">tmp:</span> <span class="pre">...</span></code>. (Contributed by Alexander Belopolsky; <a class="reference external" href="https://bugs.python.org/issue2021">bpo-2021</a>.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">test.test_support</span></code> module gained a number of context managers useful for writing tests. <code class="xref py py-func docutils literal notranslate"><span class="pre">EnvironmentVarGuard()</span></code> is a context manager that temporarily changes environment variables and automatically restores them to their old values.</p> <p>Another context manager, <code class="xref py py-class docutils literal notranslate"><span class="pre">TransientResource</span></code>, can surround calls to resources that may or may not be available; it will catch and ignore a specified list of exceptions. For example, a network test may ignore certain failures when connecting to an external web site:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">test_support</span><span class="o">.</span><span class="n">TransientResource</span><span class="p">(</span><span class="ne">IOError</span><span class="p">,</span> <span class="n">errno</span><span class="o">=</span><span class="n">errno</span><span class="o">.</span><span class="n">ETIMEDOUT</span><span class="p">):</span> <span class="n">f</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="s1">'https://sf.net'</span><span class="p">)</span> <span class="o">...</span> </pre></div> </div> <p>Finally, <code class="xref py py-func docutils literal notranslate"><span class="pre">check_warnings()</span></code> resets the <code class="xref py py-mod docutils literal notranslate"><span class="pre">warning</span></code> module’s warning filters and returns an object that will record all warning messages triggered (<a class="reference external" href="https://bugs.python.org/issue3781">bpo-3781</a>):</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">test_support</span><span class="o">.</span><span class="n">check_warnings</span><span class="p">()</span> <span class="k">as</span> <span class="n">wrec</span><span class="p">:</span> <span class="n">warnings</span><span class="o">.</span><span class="n">simplefilter</span><span class="p">(</span><span class="s2">"always"</span><span class="p">)</span> <span class="c1"># ... code that triggers a warning ...</span> <span class="k">assert</span> <span class="nb">str</span><span class="p">(</span><span class="n">wrec</span><span class="o">.</span><span class="n">message</span><span class="p">)</span> <span class="o">==</span> <span class="s2">"function is outdated"</span> <span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">wrec</span><span class="o">.</span><span class="n">warnings</span><span class="p">)</span> <span class="o">==</span> <span class="mi">1</span><span class="p">,</span> <span class="s2">"Multiple warnings raised"</span> </pre></div> </div> <p>(Contributed by Brett Cannon.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/textwrap.html#module-textwrap" title="textwrap: Text wrapping and filling"><code class="xref py py-mod docutils literal notranslate"><span class="pre">textwrap</span></code></a> module can now preserve existing whitespace at the beginnings and ends of the newly-created lines by specifying <code class="docutils literal notranslate"><span class="pre">drop_whitespace=False</span></code> as an argument:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">S</span> <span class="o">=</span> <span class="s2">"""This sentence has a bunch of</span> <span class="gp">... </span><span class="s2"> extra whitespace."""</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">textwrap</span><span class="o">.</span><span class="n">fill</span><span class="p">(</span><span class="n">S</span><span class="p">,</span> <span class="n">width</span><span class="o">=</span><span class="mi">15</span><span class="p">)</span> <span class="go">This sentence</span> <span class="go">has a bunch</span> <span class="go">of extra</span> <span class="go">whitespace.</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">textwrap</span><span class="o">.</span><span class="n">fill</span><span class="p">(</span><span class="n">S</span><span class="p">,</span> <span class="n">drop_whitespace</span><span class="o">=</span><span class="kc">False</span><span class="p">,</span> <span class="n">width</span><span class="o">=</span><span class="mi">15</span><span class="p">)</span> <span class="go">This sentence</span> <span class="go"> has a bunch</span> <span class="go"> of extra</span> <span class="go"> whitespace.</span> <span class="go">>>></span> </pre></div> </div> <p>(Contributed by Dwayne Bailey; <a class="reference external" href="https://bugs.python.org/issue1581073">bpo-1581073</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> module API is being changed to use properties such as <code class="xref py py-attr docutils literal notranslate"><span class="pre">daemon</span></code> instead of <code class="xref py py-meth docutils literal notranslate"><span class="pre">setDaemon()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">isDaemon()</span></code> methods, and some methods have been renamed to use underscores instead of camel-case; for example, the <code class="xref py py-meth docutils literal notranslate"><span class="pre">activeCount()</span></code> method is renamed to <code class="xref py py-meth docutils literal notranslate"><span class="pre">active_count()</span></code>. Both the 2.6 and 3.0 versions of the module support the same properties and renamed methods, but don’t remove the old methods. No date has been set for the deprecation of the old APIs in Python 3.x; the old APIs won’t be removed in any 2.x version. (Carried out by several people, most notably Benjamin Peterson.)</p> <p>The <a class="reference internal" href="../library/threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">Thread</span></code> objects gained an <code class="xref py py-attr docutils literal notranslate"><span class="pre">ident</span></code> property that returns the thread’s identifier, a nonzero integer. (Contributed by Gregory P. Smith; <a class="reference external" href="https://bugs.python.org/issue2871">bpo-2871</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/timeit.html#module-timeit" title="timeit: Measure the execution time of small code snippets."><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code></a> module now accepts callables as well as strings for the statement being timed and for the setup code. Two convenience functions were added for creating <code class="xref py py-class docutils literal notranslate"><span class="pre">Timer</span></code> instances: <code class="docutils literal notranslate"><span class="pre">repeat(stmt,</span> <span class="pre">setup,</span> <span class="pre">time,</span> <span class="pre">repeat,</span> <span class="pre">number)</span></code> and <code class="docutils literal notranslate"><span class="pre">timeit(stmt,</span> <span class="pre">setup,</span> <span class="pre">time,</span> <span class="pre">number)</span></code> create an instance and call the corresponding method. (Contributed by Erik Demaine; <a class="reference external" href="https://bugs.python.org/issue1533909">bpo-1533909</a>.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">Tkinter</span></code> module now accepts lists and tuples for options, separating the elements by spaces before passing the resulting value to Tcl/Tk. (Contributed by Guilherme Polo; <a class="reference external" href="https://bugs.python.org/issue2906">bpo-2906</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/turtle.html#module-turtle" title="turtle: An educational framework for simple graphics applications"><code class="xref py py-mod docutils literal notranslate"><span class="pre">turtle</span></code></a> module for turtle graphics was greatly enhanced by Gregor Lingl. New features in the module include:</p> <ul class="simple"> <li>Better animation of turtle movement and rotation.</li> <li>Control over turtle movement using the new <code class="xref py py-meth docutils literal notranslate"><span class="pre">delay()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">tracer()</span></code>, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">speed()</span></code> methods.</li> <li>The ability to set new shapes for the turtle, and to define a new coordinate system.</li> <li>Turtles now have an <code class="xref py py-meth docutils literal notranslate"><span class="pre">undo()</span></code> method that can roll back actions.</li> <li>Simple support for reacting to input events such as mouse and keyboard activity, making it possible to write simple games.</li> <li>A <code class="file docutils literal notranslate"><span class="pre">turtle.cfg</span></code> file can be used to customize the starting appearance of the turtle’s screen.</li> <li>The module’s docstrings can be replaced by new docstrings that have been translated into another language.</li> </ul> <p>(<a class="reference external" href="https://bugs.python.org/issue1513695">bpo-1513695</a>)</p> </li> <li><p class="first">An optional <code class="docutils literal notranslate"><span class="pre">timeout</span></code> parameter was added to the <code class="xref py py-func docutils literal notranslate"><span class="pre">urllib.urlopen()</span></code> function and the <code class="xref py py-class docutils literal notranslate"><span class="pre">urllib.ftpwrapper</span></code> class constructor, as well as the <code class="xref py py-func docutils literal notranslate"><span class="pre">urllib2.urlopen()</span></code> function. The parameter specifies a timeout measured in seconds. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">u</span> <span class="o">=</span> <span class="n">urllib2</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="s2">"http://slow.example.com"</span><span class="p">,</span> <span class="go"> timeout=3)</span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">urllib2.URLError</span>: <span class="n"><urlopen error timed out></span> <span class="go">>>></span> </pre></div> </div> <p>(Added by Facundo Batista.)</p> </li> <li><p class="first">The Unicode database provided by the <a class="reference internal" href="../library/unicodedata.html#module-unicodedata" title="unicodedata: Access the Unicode Database."><code class="xref py py-mod docutils literal notranslate"><span class="pre">unicodedata</span></code></a> module has been updated to version 5.1.0. (Updated by Martin von Löwis; <a class="reference external" href="https://bugs.python.org/issue3811">bpo-3811</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate"><span class="pre">warnings</span></code></a> module’s <code class="xref py py-func docutils literal notranslate"><span class="pre">formatwarning()</span></code> and <code class="xref py py-func docutils literal notranslate"><span class="pre">showwarning()</span></code> gained an optional <em>line</em> argument that can be used to supply the line of source code. (Added as part of <a class="reference external" href="https://bugs.python.org/issue1631171">bpo-1631171</a>, which re-implemented part of the <a class="reference internal" href="../library/warnings.html#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate"><span class="pre">warnings</span></code></a> module in C code.)</p> <p>A new function, <code class="xref py py-func docutils literal notranslate"><span class="pre">catch_warnings()</span></code>, is a context manager intended for testing purposes that lets you temporarily modify the warning filters and then restore their original values (<a class="reference external" href="https://bugs.python.org/issue3781">bpo-3781</a>).</p> </li> <li><p class="first">The XML-RPC <code class="xref py py-class docutils literal notranslate"><span class="pre">SimpleXMLRPCServer</span></code> and <code class="xref py py-class docutils literal notranslate"><span class="pre">DocXMLRPCServer</span></code> classes can now be prevented from immediately opening and binding to their socket by passing <code class="docutils literal notranslate"><span class="pre">False</span></code> as the <em>bind_and_activate</em> constructor parameter. This can be used to modify the instance’s <code class="xref py py-attr docutils literal notranslate"><span class="pre">allow_reuse_address</span></code> attribute before calling the <code class="xref py py-meth docutils literal notranslate"><span class="pre">server_bind()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">server_activate()</span></code> methods to open the socket and begin listening for connections. (Contributed by Peter Parente; <a class="reference external" href="https://bugs.python.org/issue1599845">bpo-1599845</a>.)</p> <p><code class="xref py py-class docutils literal notranslate"><span class="pre">SimpleXMLRPCServer</span></code> also has a <code class="xref py py-attr docutils literal notranslate"><span class="pre">_send_traceback_header</span></code> attribute; if true, the exception and formatted traceback are returned as HTTP headers “X-Exception” and “X-Traceback”. This feature is for debugging purposes only and should not be used on production servers because the tracebacks might reveal passwords or other sensitive information. (Contributed by Alan McIntyre as part of his project for Google’s Summer of Code 2007.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">xmlrpclib</span></code> module no longer automatically converts <a class="reference internal" href="../library/datetime.html#datetime.date" title="datetime.date"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime.date</span></code></a> and <a class="reference internal" href="../library/datetime.html#datetime.time" title="datetime.time"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime.time</span></code></a> to the <code class="xref py py-class docutils literal notranslate"><span class="pre">xmlrpclib.DateTime</span></code> type; the conversion semantics were not necessarily correct for all applications. Code using <code class="xref py py-mod docutils literal notranslate"><span class="pre">xmlrpclib</span></code> should convert <code class="xref py py-class docutils literal notranslate"><span class="pre">date</span></code> and <a class="reference internal" href="../library/datetime.html#datetime.time" title="datetime.time"><code class="xref py py-class docutils literal notranslate"><span class="pre">time</span></code></a> instances. (<a class="reference external" href="https://bugs.python.org/issue1330538">bpo-1330538</a>) The code can also handle dates before 1900 (contributed by Ralf Schmitt; <a class="reference external" href="https://bugs.python.org/issue2014">bpo-2014</a>) and 64-bit integers represented by using <code class="docutils literal notranslate"><span class="pre"><i8></span></code> in XML-RPC responses (contributed by Riku Lindblad; <a class="reference external" href="https://bugs.python.org/issue2985">bpo-2985</a>).</p> </li> <li><p class="first">The <a class="reference internal" href="../library/zipfile.html#module-zipfile" title="zipfile: Read and write ZIP-format archive files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zipfile</span></code></a> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">ZipFile</span></code> class now has <code class="xref py py-meth docutils literal notranslate"><span class="pre">extract()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">extractall()</span></code> methods that will unpack a single file or all the files in the archive to the current directory, or to a specified directory:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">z</span> <span class="o">=</span> <span class="n">zipfile</span><span class="o">.</span><span class="n">ZipFile</span><span class="p">(</span><span class="s1">'python-251.zip'</span><span class="p">)</span> <span class="c1"># Unpack a single file, writing it relative</span> <span class="c1"># to the /tmp directory.</span> <span class="n">z</span><span class="o">.</span><span class="n">extract</span><span class="p">(</span><span class="s1">'Python/sysmodule.c'</span><span class="p">,</span> <span class="s1">'/tmp'</span><span class="p">)</span> <span class="c1"># Unpack all the files in the archive.</span> <span class="n">z</span><span class="o">.</span><span class="n">extractall</span><span class="p">()</span> </pre></div> </div> <p>(Contributed by Alan McIntyre; <a class="reference external" href="https://bugs.python.org/issue467924">bpo-467924</a>.)</p> <p>The <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-meth docutils literal notranslate"><span class="pre">open()</span></code></a>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">extract()</span></code> methods can now take either a filename or a <code class="xref py py-class docutils literal notranslate"><span class="pre">ZipInfo</span></code> object. This is useful when an archive accidentally contains a duplicated filename. (Contributed by Graham Horler; <a class="reference external" href="https://bugs.python.org/issue1775025">bpo-1775025</a>.)</p> <p>Finally, <a class="reference internal" href="../library/zipfile.html#module-zipfile" title="zipfile: Read and write ZIP-format archive files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zipfile</span></code></a> now supports using Unicode filenames for archived files. (Contributed by Alexey Borzenkov; <a class="reference external" href="https://bugs.python.org/issue1734346">bpo-1734346</a>.)</p> </li> </ul> <div class="section" id="the-ast-module"> <h3>The <a class="reference internal" href="../library/ast.html#module-ast" title="ast: Abstract Syntax Tree classes and manipulation."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ast</span></code></a> module<a class="headerlink" href="#the-ast-module" title="Permalink to this headline">¶</a></h3> <p>The <a class="reference internal" href="../library/ast.html#module-ast" title="ast: Abstract Syntax Tree classes and manipulation."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ast</span></code></a> module provides an Abstract Syntax Tree representation of Python code, and Armin Ronacher contributed a set of helper functions that perform a variety of common tasks. These will be useful for HTML templating packages, code analyzers, and similar tools that process Python code.</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">parse()</span></code> function takes an expression and returns an AST. The <code class="xref py py-func docutils literal notranslate"><span class="pre">dump()</span></code> function outputs a representation of a tree, suitable for debugging:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">ast</span> <span class="n">t</span> <span class="o">=</span> <span class="n">ast</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="s2">"""</span> <span class="s2">d = </span><span class="si">{}</span><span class="s2"></span> <span class="s2">for i in 'abcdefghijklm':</span> <span class="s2"> d[i + i] = ord(i) - ord('a') + 1</span> <span class="s2">print d</span> <span class="s2">"""</span><span class="p">)</span> <span class="nb">print</span> <span class="n">ast</span><span class="o">.</span><span class="n">dump</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> </pre></div> </div> <p>This outputs a deeply nested tree:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">Module</span><span class="p">(</span><span class="n">body</span><span class="o">=</span><span class="p">[</span> <span class="n">Assign</span><span class="p">(</span><span class="n">targets</span><span class="o">=</span><span class="p">[</span> <span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'d'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Store</span><span class="p">())</span> <span class="p">],</span> <span class="n">value</span><span class="o">=</span><span class="n">Dict</span><span class="p">(</span><span class="n">keys</span><span class="o">=</span><span class="p">[],</span> <span class="n">values</span><span class="o">=</span><span class="p">[]))</span> <span class="n">For</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'i'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Store</span><span class="p">()),</span> <span class="nb">iter</span><span class="o">=</span><span class="n">Str</span><span class="p">(</span><span class="n">s</span><span class="o">=</span><span class="s1">'abcdefghijklm'</span><span class="p">),</span> <span class="n">body</span><span class="o">=</span><span class="p">[</span> <span class="n">Assign</span><span class="p">(</span><span class="n">targets</span><span class="o">=</span><span class="p">[</span> <span class="n">Subscript</span><span class="p">(</span><span class="n">value</span><span class="o">=</span> <span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'d'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Load</span><span class="p">()),</span> <span class="nb">slice</span><span class="o">=</span> <span class="n">Index</span><span class="p">(</span><span class="n">value</span><span class="o">=</span> <span class="n">BinOp</span><span class="p">(</span><span class="n">left</span><span class="o">=</span><span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'i'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Load</span><span class="p">()),</span> <span class="n">op</span><span class="o">=</span><span class="n">Add</span><span class="p">(),</span> <span class="n">right</span><span class="o">=</span><span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'i'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Load</span><span class="p">()))),</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Store</span><span class="p">())</span> <span class="p">],</span> <span class="n">value</span><span class="o">=</span> <span class="n">BinOp</span><span class="p">(</span><span class="n">left</span><span class="o">=</span> <span class="n">BinOp</span><span class="p">(</span><span class="n">left</span><span class="o">=</span> <span class="n">Call</span><span class="p">(</span><span class="n">func</span><span class="o">=</span> <span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'ord'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Load</span><span class="p">()),</span> <span class="n">args</span><span class="o">=</span><span class="p">[</span> <span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'i'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Load</span><span class="p">())</span> <span class="p">],</span> <span class="n">keywords</span><span class="o">=</span><span class="p">[],</span> <span class="n">starargs</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">kwargs</span><span class="o">=</span><span class="kc">None</span><span class="p">),</span> <span class="n">op</span><span class="o">=</span><span class="n">Sub</span><span class="p">(),</span> <span class="n">right</span><span class="o">=</span><span class="n">Call</span><span class="p">(</span><span class="n">func</span><span class="o">=</span> <span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'ord'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Load</span><span class="p">()),</span> <span class="n">args</span><span class="o">=</span><span class="p">[</span> <span class="n">Str</span><span class="p">(</span><span class="n">s</span><span class="o">=</span><span class="s1">'a'</span><span class="p">)</span> <span class="p">],</span> <span class="n">keywords</span><span class="o">=</span><span class="p">[],</span> <span class="n">starargs</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">kwargs</span><span class="o">=</span><span class="kc">None</span><span class="p">)),</span> <span class="n">op</span><span class="o">=</span><span class="n">Add</span><span class="p">(),</span> <span class="n">right</span><span class="o">=</span><span class="n">Num</span><span class="p">(</span><span class="n">n</span><span class="o">=</span><span class="mi">1</span><span class="p">)))</span> <span class="p">],</span> <span class="n">orelse</span><span class="o">=</span><span class="p">[])</span> <span class="n">Print</span><span class="p">(</span><span class="n">dest</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">values</span><span class="o">=</span><span class="p">[</span> <span class="n">Name</span><span class="p">(</span><span class="nb">id</span><span class="o">=</span><span class="s1">'d'</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="n">Load</span><span class="p">())</span> <span class="p">],</span> <span class="n">nl</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="p">])</span> </pre></div> </div> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">literal_eval()</span></code> method takes a string or an AST representing a literal expression, parses and evaluates it, and returns the resulting value. A literal expression is a Python expression containing only strings, numbers, dictionaries, etc. but no statements or function calls. If you need to evaluate an expression but cannot accept the security risk of using an <a class="reference internal" href="../library/functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate"><span class="pre">eval()</span></code></a> call, <code class="xref py py-func docutils literal notranslate"><span class="pre">literal_eval()</span></code> will handle it safely:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">literal</span> <span class="o">=</span> <span class="s1">'("a", "b", {2:4, 3:8, 1:2})'</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">ast</span><span class="o">.</span><span class="n">literal_eval</span><span class="p">(</span><span class="n">literal</span><span class="p">)</span> <span class="go">('a', 'b', {1: 2, 2: 4, 3: 8})</span> <span class="gp">>>> </span><span class="nb">print</span> <span class="n">ast</span><span class="o">.</span><span class="n">literal_eval</span><span class="p">(</span><span class="s1">'"a" + "b"'</span><span class="p">)</span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">ValueError</span>: <span class="n">malformed string</span> </pre></div> </div> <p>The module also includes <code class="xref py py-class docutils literal notranslate"><span class="pre">NodeVisitor</span></code> and <code class="xref py py-class docutils literal notranslate"><span class="pre">NodeTransformer</span></code> classes for traversing and modifying an AST, and functions for common transformations such as changing line numbers.</p> </div> <div class="section" id="the-future-builtins-module"> <h3>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">future_builtins</span></code> module<a class="headerlink" href="#the-future-builtins-module" title="Permalink to this headline">¶</a></h3> <p>Python 3.0 makes many changes to the repertoire of built-in functions, and most of the changes can’t be introduced in the Python 2.x series because they would break compatibility. The <code class="xref py py-mod docutils literal notranslate"><span class="pre">future_builtins</span></code> module provides versions of these built-in functions that can be imported when writing 3.0-compatible code.</p> <p>The functions in this module currently include:</p> <ul class="simple"> <li><code class="docutils literal notranslate"><span class="pre">ascii(obj)</span></code>: equivalent to <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a>. In Python 3.0, <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> will return a Unicode string, while <a class="reference internal" href="../library/functions.html#ascii" title="ascii"><code class="xref py py-func docutils literal notranslate"><span class="pre">ascii()</span></code></a> will return a pure ASCII bytestring.</li> <li><code class="docutils literal notranslate"><span class="pre">filter(predicate,</span> <span class="pre">iterable)</span></code>, <code class="docutils literal notranslate"><span class="pre">map(func,</span> <span class="pre">iterable1,</span> <span class="pre">...)</span></code>: the 3.0 versions return iterators, unlike the 2.x builtins which return lists.</li> <li><code class="docutils literal notranslate"><span class="pre">hex(value)</span></code>, <code class="docutils literal notranslate"><span class="pre">oct(value)</span></code>: instead of calling the <code class="xref py py-meth docutils literal notranslate"><span class="pre">__hex__()</span></code> or <code class="xref py py-meth docutils literal notranslate"><span class="pre">__oct__()</span></code> methods, these versions will call the <a class="reference internal" href="../reference/datamodel.html#object.__index__" title="object.__index__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__index__()</span></code></a> method and convert the result to hexadecimal or octal. <a class="reference internal" href="../library/functions.html#oct" title="oct"><code class="xref py py-func docutils literal notranslate"><span class="pre">oct()</span></code></a> will use the new <code class="docutils literal notranslate"><span class="pre">0o</span></code> notation for its result.</li> </ul> </div> <div class="section" id="the-json-module-javascript-object-notation"> <h3>The <a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> module: JavaScript Object Notation<a class="headerlink" href="#the-json-module-javascript-object-notation" title="Permalink to this headline">¶</a></h3> <p>The new <a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> module supports the encoding and decoding of Python types in JSON (Javascript Object Notation). JSON is a lightweight interchange format often used in web applications. For more information about JSON, see <a class="reference external" href="http://www.json.org">http://www.json.org</a>.</p> <p><a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> comes with support for decoding and encoding most built-in Python types. The following example encodes and decodes a dictionary:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">json</span> <span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="p">{</span><span class="s2">"spam"</span><span class="p">:</span> <span class="s2">"foo"</span><span class="p">,</span> <span class="s2">"parrot"</span><span class="p">:</span> <span class="mi">42</span><span class="p">}</span> <span class="gp">>>> </span><span class="n">in_json</span> <span class="o">=</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="n">data</span><span class="p">)</span> <span class="c1"># Encode the data</span> <span class="gp">>>> </span><span class="n">in_json</span> <span class="go">'{"parrot": 42, "spam": "foo"}'</span> <span class="gp">>>> </span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="n">in_json</span><span class="p">)</span> <span class="c1"># Decode into a Python object</span> <span class="go">{"spam": "foo", "parrot": 42}</span> </pre></div> </div> <p>It’s also possible to write your own decoders and encoders to support more types. Pretty-printing of the JSON strings is also supported.</p> <p><a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> (originally called simplejson) was written by Bob Ippolito.</p> </div> <div class="section" id="the-plistlib-module-a-property-list-parser"> <h3>The <a class="reference internal" href="../library/plistlib.html#module-plistlib" title="plistlib: Generate and parse Mac OS X plist files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">plistlib</span></code></a> module: A Property-List Parser<a class="headerlink" href="#the-plistlib-module-a-property-list-parser" title="Permalink to this headline">¶</a></h3> <p>The <code class="docutils literal notranslate"><span class="pre">.plist</span></code> format is commonly used on Mac OS X to store basic data types (numbers, strings, lists, and dictionaries) by serializing them into an XML-based format. It resembles the XML-RPC serialization of data types.</p> <p>Despite being primarily used on Mac OS X, the format has nothing Mac-specific about it and the Python implementation works on any platform that Python supports, so the <a class="reference internal" href="../library/plistlib.html#module-plistlib" title="plistlib: Generate and parse Mac OS X plist files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">plistlib</span></code></a> module has been promoted to the standard library.</p> <p>Using the module is simple:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">sys</span> <span class="kn">import</span> <span class="nn">plistlib</span> <span class="kn">import</span> <span class="nn">datetime</span> <span class="c1"># Create data structure</span> <span class="n">data_struct</span> <span class="o">=</span> <span class="nb">dict</span><span class="p">(</span><span class="n">lastAccessed</span><span class="o">=</span><span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="o">.</span><span class="n">now</span><span class="p">(),</span> <span class="n">version</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">categories</span><span class="o">=</span><span class="p">(</span><span class="s1">'Personal'</span><span class="p">,</span><span class="s1">'Shared'</span><span class="p">,</span><span class="s1">'Private'</span><span class="p">))</span> <span class="c1"># Create string containing XML.</span> <span class="n">plist_str</span> <span class="o">=</span> <span class="n">plistlib</span><span class="o">.</span><span class="n">writePlistToString</span><span class="p">(</span><span class="n">data_struct</span><span class="p">)</span> <span class="n">new_struct</span> <span class="o">=</span> <span class="n">plistlib</span><span class="o">.</span><span class="n">readPlistFromString</span><span class="p">(</span><span class="n">plist_str</span><span class="p">)</span> <span class="nb">print</span> <span class="n">data_struct</span> <span class="nb">print</span> <span class="n">new_struct</span> <span class="c1"># Write data structure to a file and read it back.</span> <span class="n">plistlib</span><span class="o">.</span><span class="n">writePlist</span><span class="p">(</span><span class="n">data_struct</span><span class="p">,</span> <span class="s1">'/tmp/customizations.plist'</span><span class="p">)</span> <span class="n">new_struct</span> <span class="o">=</span> <span class="n">plistlib</span><span class="o">.</span><span class="n">readPlist</span><span class="p">(</span><span class="s1">'/tmp/customizations.plist'</span><span class="p">)</span> <span class="c1"># read/writePlist accepts file-like objects as well as paths.</span> <span class="n">plistlib</span><span class="o">.</span><span class="n">writePlist</span><span class="p">(</span><span class="n">data_struct</span><span class="p">,</span> <span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span> </pre></div> </div> </div> <div class="section" id="ctypes-enhancements"> <h3>ctypes Enhancements<a class="headerlink" href="#ctypes-enhancements" title="Permalink to this headline">¶</a></h3> <p>Thomas Heller continued to maintain and enhance the <a class="reference internal" href="../library/ctypes.html#module-ctypes" title="ctypes: A foreign function library for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ctypes</span></code></a> module.</p> <p><a class="reference internal" href="../library/ctypes.html#module-ctypes" title="ctypes: A foreign function library for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ctypes</span></code></a> now supports a <code class="xref py py-class docutils literal notranslate"><span class="pre">c_bool</span></code> datatype that represents the C99 <code class="docutils literal notranslate"><span class="pre">bool</span></code> type. (Contributed by David Remahl; <a class="reference external" href="https://bugs.python.org/issue1649190">bpo-1649190</a>.)</p> <p>The <a class="reference internal" href="../library/ctypes.html#module-ctypes" title="ctypes: A foreign function library for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ctypes</span></code></a> string, buffer and array types have improved support for extended slicing syntax, where various combinations of <code class="docutils literal notranslate"><span class="pre">(start,</span> <span class="pre">stop,</span> <span class="pre">step)</span></code> are supplied. (Implemented by Thomas Wouters.)</p> <p>All <a class="reference internal" href="../library/ctypes.html#module-ctypes" title="ctypes: A foreign function library for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ctypes</span></code></a> data types now support <code class="xref py py-meth docutils literal notranslate"><span class="pre">from_buffer()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">from_buffer_copy()</span></code> methods that create a ctypes instance based on a provided buffer object. <code class="xref py py-meth docutils literal notranslate"><span class="pre">from_buffer_copy()</span></code> copies the contents of the object, while <code class="xref py py-meth docutils literal notranslate"><span class="pre">from_buffer()</span></code> will share the same memory area.</p> <p>A new calling convention tells <a class="reference internal" href="../library/ctypes.html#module-ctypes" title="ctypes: A foreign function library for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ctypes</span></code></a> to clear the <code class="docutils literal notranslate"><span class="pre">errno</span></code> or Win32 LastError variables at the outset of each wrapped call. (Implemented by Thomas Heller; <a class="reference external" href="https://bugs.python.org/issue1798">bpo-1798</a>.)</p> <p>You can now retrieve the Unix <code class="docutils literal notranslate"><span class="pre">errno</span></code> variable after a function call. When creating a wrapped function, you can supply <code class="docutils literal notranslate"><span class="pre">use_errno=True</span></code> as a keyword parameter to the <code class="xref py py-func docutils literal notranslate"><span class="pre">DLL()</span></code> function and then call the module-level methods <code class="xref py py-meth docutils literal notranslate"><span class="pre">set_errno()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">get_errno()</span></code> to set and retrieve the error value.</p> <p>The Win32 LastError variable is similarly supported by the <code class="xref py py-func docutils literal notranslate"><span class="pre">DLL()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">OleDLL()</span></code>, and <code class="xref py py-func docutils literal notranslate"><span class="pre">WinDLL()</span></code> functions. You supply <code class="docutils literal notranslate"><span class="pre">use_last_error=True</span></code> as a keyword parameter and then call the module-level methods <code class="xref py py-meth docutils literal notranslate"><span class="pre">set_last_error()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">get_last_error()</span></code>.</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">byref()</span></code> function, used to retrieve a pointer to a ctypes instance, now has an optional <em>offset</em> parameter that is a byte count that will be added to the returned pointer.</p> </div> <div class="section" id="improved-ssl-support"> <h3>Improved SSL Support<a class="headerlink" href="#improved-ssl-support" title="Permalink to this headline">¶</a></h3> <p>Bill Janssen made extensive improvements to Python 2.6’s support for the Secure Sockets Layer by adding a new module, <a class="reference internal" href="../library/ssl.html#module-ssl" title="ssl: TLS/SSL wrapper for socket objects"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ssl</span></code></a>, that’s built atop the <a class="reference external" href="https://www.openssl.org/">OpenSSL</a> library. This new module provides more control over the protocol negotiated, the X.509 certificates used, and has better support for writing SSL servers (as opposed to clients) in Python. The existing SSL support in the <a class="reference internal" href="../library/socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> module hasn’t been removed and continues to work, though it will be removed in Python 3.0.</p> <p>To use the new module, you must first create a TCP connection in the usual way and then pass it to the <a class="reference internal" href="../library/ssl.html#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">ssl.wrap_socket()</span></code></a> function. It’s possible to specify whether a certificate is required, and to obtain certificate info by calling the <code class="xref py py-meth docutils literal notranslate"><span class="pre">getpeercert()</span></code> method.</p> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <p class="last">The documentation for the <a class="reference internal" href="../library/ssl.html#module-ssl" title="ssl: TLS/SSL wrapper for socket objects"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ssl</span></code></a> module.</p> </div> </div> </div> <div class="section" id="deprecations-and-removals"> <h2>Deprecations and Removals<a class="headerlink" href="#deprecations-and-removals" title="Permalink to this headline">¶</a></h2> <ul> <li><p class="first">String exceptions have been removed. Attempting to use them raises a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p> </li> <li><p class="first">Changes to the <a class="reference internal" href="../library/exceptions.html#Exception" title="Exception"><code class="xref py py-class docutils literal notranslate"><span class="pre">Exception</span></code></a> interface as dictated by <span class="target" id="index-25"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0352"><strong>PEP 352</strong></a> continue to be made. For 2.6, the <code class="xref py py-attr docutils literal notranslate"><span class="pre">message</span></code> attribute is being deprecated in favor of the <code class="xref py py-attr docutils literal notranslate"><span class="pre">args</span></code> attribute.</p> </li> <li><p class="first">(3.0-warning mode) Python 3.0 will feature a reorganized standard library that will drop many outdated modules and rename others. Python 2.6 running in 3.0-warning mode will warn about these modules when they are imported.</p> <p>The list of deprecated modules is: <code class="xref py py-mod docutils literal notranslate"><span class="pre">audiodev</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">bgenlocations</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">buildtools</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">bundlebuilder</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Canvas</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">compiler</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">dircache</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">fpformat</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">gensuitemodule</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">ihooks</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">imageop</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">imgfile</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">linuxaudiodev</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">mhlib</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">mimetools</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">multifile</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">new</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">pure</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">statvfs</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">sunaudiodev</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">test.testall</span></code>, and <code class="xref py py-mod docutils literal notranslate"><span class="pre">toaiff</span></code>.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">gopherlib</span></code> module has been removed.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">MimeWriter</span></code> module and <code class="xref py py-mod docutils literal notranslate"><span class="pre">mimify</span></code> module have been deprecated; use the <a class="reference internal" href="../library/email.html#module-email" title="email: Package supporting the parsing, manipulating, and generating email messages."><code class="xref py py-mod docutils literal notranslate"><span class="pre">email</span></code></a> package instead.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">md5</span></code> module has been deprecated; use the <a class="reference internal" href="../library/hashlib.html#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><code class="xref py py-mod docutils literal notranslate"><span class="pre">hashlib</span></code></a> module instead.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">posixfile</span></code> module has been deprecated; <a class="reference internal" href="../library/fcntl.html#fcntl.lockf" title="fcntl.lockf"><code class="xref py py-func docutils literal notranslate"><span class="pre">fcntl.lockf()</span></code></a> provides better locking.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">popen2</span></code> module has been deprecated; use the <a class="reference internal" href="../library/subprocess.html#module-subprocess" title="subprocess: Subprocess management."><code class="xref py py-mod docutils literal notranslate"><span class="pre">subprocess</span></code></a> module.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">rgbimg</span></code> module has been removed.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">sets</span></code> module has been deprecated; it’s better to use the built-in <a class="reference internal" href="../library/stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate"><span class="pre">set</span></code></a> and <a class="reference internal" href="../library/stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate"><span class="pre">frozenset</span></code></a> types.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">sha</span></code> module has been deprecated; use the <a class="reference internal" href="../library/hashlib.html#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><code class="xref py py-mod docutils literal notranslate"><span class="pre">hashlib</span></code></a> module instead.</p> </li> </ul> </div> <div class="section" id="build-and-c-api-changes"> <h2>Build and C API Changes<a class="headerlink" href="#build-and-c-api-changes" title="Permalink to this headline">¶</a></h2> <p>Changes to Python’s build process and to the C API include:</p> <ul> <li><p class="first">Python now must be compiled with C89 compilers (after 19 years!). This means that the Python source tree has dropped its own implementations of <code class="xref c c-func docutils literal notranslate"><span class="pre">memmove()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">strerror()</span></code>, which are in the C89 standard library.</p> </li> <li><p class="first">Python 2.6 can be built with Microsoft Visual Studio 2008 (version 9.0), and this is the new default compiler. See the <code class="file docutils literal notranslate"><span class="pre">PCbuild</span></code> directory for the build files. (Implemented by Christian Heimes.)</p> </li> <li><p class="first">On Mac OS X, Python 2.6 can be compiled as a 4-way universal build. The <strong class="program">configure</strong> script can take a <code class="xref std std-option docutils literal notranslate"><span class="pre">--with-universal-archs=[32-bit|64-bit|all]</span></code> switch, controlling whether the binaries are built for 32-bit architectures (x86, PowerPC), 64-bit (x86-64 and PPC-64), or both. (Contributed by Ronald Oussoren.)</p> </li> <li><p class="first">The BerkeleyDB module now has a C API object, available as <code class="docutils literal notranslate"><span class="pre">bsddb.db.api</span></code>. This object can be used by other C extensions that wish to use the <code class="xref py py-mod docutils literal notranslate"><span class="pre">bsddb</span></code> module for their own purposes. (Contributed by Duncan Grisby.)</p> </li> <li><p class="first">The new buffer interface, previously described in <a class="reference external" href="#pep-3118-revised-buffer-protocol">the PEP 3118 section</a>, adds <a class="reference internal" href="../c-api/buffer.html#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a> and <a class="reference internal" href="../c-api/buffer.html#c.PyBuffer_Release" title="PyBuffer_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_Release()</span></code></a>, as well as a few other functions.</p> </li> <li><p class="first">Python’s use of the C stdio library is now thread-safe, or at least as thread-safe as the underlying library is. A long-standing potential bug occurred if one thread closed a file object while another thread was reading from or writing to the object. In 2.6 file objects have a reference count, manipulated by the <code class="xref c c-func docutils literal notranslate"><span class="pre">PyFile_IncUseCount()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">PyFile_DecUseCount()</span></code> functions. File objects can’t be closed unless the reference count is zero. <code class="xref c c-func docutils literal notranslate"><span class="pre">PyFile_IncUseCount()</span></code> should be called while the GIL is still held, before carrying out an I/O operation using the <code class="docutils literal notranslate"><span class="pre">FILE</span> <span class="pre">*</span></code> pointer, and <code class="xref c c-func docutils literal notranslate"><span class="pre">PyFile_DecUseCount()</span></code> should be called immediately after the GIL is re-acquired. (Contributed by Antoine Pitrou and Gregory P. Smith.)</p> </li> <li><p class="first">Importing modules simultaneously in two different threads no longer deadlocks; it will now raise an <a class="reference internal" href="../library/exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ImportError</span></code></a>. A new API function, <a class="reference internal" href="../c-api/import.html#c.PyImport_ImportModuleNoBlock" title="PyImport_ImportModuleNoBlock"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyImport_ImportModuleNoBlock()</span></code></a>, will look for a module in <code class="docutils literal notranslate"><span class="pre">sys.modules</span></code> first, then try to import it after acquiring an import lock. If the import lock is held by another thread, an <a class="reference internal" href="../library/exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ImportError</span></code></a> is raised. (Contributed by Christian Heimes.)</p> </li> <li><p class="first">Several functions return information about the platform’s floating-point support. <a class="reference internal" href="../c-api/float.html#c.PyFloat_GetMax" title="PyFloat_GetMax"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyFloat_GetMax()</span></code></a> returns the maximum representable floating point value, and <a class="reference internal" href="../c-api/float.html#c.PyFloat_GetMin" title="PyFloat_GetMin"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyFloat_GetMin()</span></code></a> returns the minimum positive value. <a class="reference internal" href="../c-api/float.html#c.PyFloat_GetInfo" title="PyFloat_GetInfo"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyFloat_GetInfo()</span></code></a> returns an object containing more information from the <code class="file docutils literal notranslate"><span class="pre">float.h</span></code> file, such as <code class="docutils literal notranslate"><span class="pre">"mant_dig"</span></code> (number of digits in the mantissa), <code class="docutils literal notranslate"><span class="pre">"epsilon"</span></code> (smallest difference between 1.0 and the next largest value representable), and several others. (Contributed by Christian Heimes; <a class="reference external" href="https://bugs.python.org/issue1534">bpo-1534</a>.)</p> </li> <li><p class="first">C functions and methods that use <a class="reference internal" href="../c-api/complex.html#c.PyComplex_AsCComplex" title="PyComplex_AsCComplex"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyComplex_AsCComplex()</span></code></a> will now accept arguments that have a <a class="reference internal" href="../reference/datamodel.html#object.__complex__" title="object.__complex__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__complex__()</span></code></a> method. In particular, the functions in the <a class="reference internal" href="../library/cmath.html#module-cmath" title="cmath: Mathematical functions for complex numbers."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cmath</span></code></a> module will now accept objects with this method. This is a backport of a Python 3.0 change. (Contributed by Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue1675423">bpo-1675423</a>.)</p> </li> <li><p class="first">Python’s C API now includes two functions for case-insensitive string comparisons, <code class="docutils literal notranslate"><span class="pre">PyOS_stricmp(char*,</span> <span class="pre">char*)</span></code> and <code class="docutils literal notranslate"><span class="pre">PyOS_strnicmp(char*,</span> <span class="pre">char*,</span> <span class="pre">Py_ssize_t)</span></code>. (Contributed by Christian Heimes; <a class="reference external" href="https://bugs.python.org/issue1635">bpo-1635</a>.)</p> </li> <li><p class="first">Many C extensions define their own little macro for adding integers and strings to the module’s dictionary in the <code class="docutils literal notranslate"><span class="pre">init*</span></code> function. Python 2.6 finally defines standard macros for adding values to a module, <a class="reference internal" href="../c-api/module.html#c.PyModule_AddStringMacro" title="PyModule_AddStringMacro"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyModule_AddStringMacro</span></code></a> and <code class="xref c c-macro docutils literal notranslate"><span class="pre">PyModule_AddIntMacro()</span></code>. (Contributed by Christian Heimes.)</p> </li> <li><p class="first">Some macros were renamed in both 3.0 and 2.6 to make it clearer that they are macros, not functions. <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_Size()</span></code> became <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_SIZE()</span></code>, <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_Type()</span></code> became <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_TYPE()</span></code>, and <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_Refcnt()</span></code> became <code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_REFCNT()</span></code>. The mixed-case macros are still available in Python 2.6 for backward compatibility. (<a class="reference external" href="https://bugs.python.org/issue1629">bpo-1629</a>)</p> </li> <li><p class="first">Distutils now places C extensions it builds in a different directory when running on a debug version of Python. (Contributed by Collin Winter; <a class="reference external" href="https://bugs.python.org/issue1530959">bpo-1530959</a>.)</p> </li> <li><p class="first">Several basic data types, such as integers and strings, maintain internal free lists of objects that can be re-used. The data structures for these free lists now follow a naming convention: the variable is always named <code class="docutils literal notranslate"><span class="pre">free_list</span></code>, the counter is always named <code class="docutils literal notranslate"><span class="pre">numfree</span></code>, and a macro <code class="docutils literal notranslate"><span class="pre">Py<typename>_MAXFREELIST</span></code> is always defined.</p> </li> <li><p class="first">A new Makefile target, “make patchcheck”, prepares the Python source tree for making a patch: it fixes trailing whitespace in all modified <code class="docutils literal notranslate"><span class="pre">.py</span></code> files, checks whether the documentation has been changed, and reports whether the <code class="file docutils literal notranslate"><span class="pre">Misc/ACKS</span></code> and <code class="file docutils literal notranslate"><span class="pre">Misc/NEWS</span></code> files have been updated. (Contributed by Brett Cannon.)</p> <p>Another new target, “make profile-opt”, compiles a Python binary using GCC’s profile-guided optimization. It compiles Python with profiling enabled, runs the test suite to obtain a set of profiling results, and then compiles using these results for optimization. (Contributed by Gregory P. Smith.)</p> </li> </ul> <div class="section" id="port-specific-changes-windows"> <h3>Port-Specific Changes: Windows<a class="headerlink" href="#port-specific-changes-windows" title="Permalink to this headline">¶</a></h3> <ul> <li><p class="first">The support for Windows 95, 98, ME and NT4 has been dropped. Python 2.6 requires at least Windows 2000 SP4.</p> </li> <li><p class="first">The new default compiler on Windows is Visual Studio 2008 (version 9.0). The build directories for Visual Studio 2003 (version 7.1) and 2005 (version 8.0) were moved into the PC/ directory. The new <code class="file docutils literal notranslate"><span class="pre">PCbuild</span></code> directory supports cross compilation for X64, debug builds and Profile Guided Optimization (PGO). PGO builds are roughly 10% faster than normal builds. (Contributed by Christian Heimes with help from Amaury Forgeot d’Arc and Martin von Löwis.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/msvcrt.html#module-msvcrt" title="msvcrt: Miscellaneous useful routines from the MS VC++ runtime. (Windows)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">msvcrt</span></code></a> module now supports both the normal and wide char variants of the console I/O API. The <code class="xref py py-func docutils literal notranslate"><span class="pre">getwch()</span></code> function reads a keypress and returns a Unicode value, as does the <code class="xref py py-func docutils literal notranslate"><span class="pre">getwche()</span></code> function. The <code class="xref py py-func docutils literal notranslate"><span class="pre">putwch()</span></code> function takes a Unicode character and writes it to the console. (Contributed by Christian Heimes.)</p> </li> <li><p class="first"><a class="reference internal" href="../library/os.path.html#os.path.expandvars" title="os.path.expandvars"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.path.expandvars()</span></code></a> will now expand environment variables in the form “%var%”, and “~user” will be expanded into the user’s home directory path. (Contributed by Josiah Carlson; <a class="reference external" href="https://bugs.python.org/issue957650">bpo-957650</a>.)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> module’s socket objects now have an <code class="xref py py-meth docutils literal notranslate"><span class="pre">ioctl()</span></code> method that provides a limited interface to the <code class="xref c c-func docutils literal notranslate"><span class="pre">WSAIoctl()</span></code> system interface.</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">_winreg</span></code> module now has a function, <code class="xref py py-func docutils literal notranslate"><span class="pre">ExpandEnvironmentStrings()</span></code>, that expands environment variable references such as <code class="docutils literal notranslate"><span class="pre">%NAME%</span></code> in an input string. The handle objects provided by this module now support the context protocol, so they can be used in <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statements. (Contributed by Christian Heimes.)</p> <p><code class="xref py py-mod docutils literal notranslate"><span class="pre">_winreg</span></code> also has better support for x64 systems, exposing the <code class="xref py py-func docutils literal notranslate"><span class="pre">DisableReflectionKey()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">EnableReflectionKey()</span></code>, and <code class="xref py py-func docutils literal notranslate"><span class="pre">QueryReflectionKey()</span></code> functions, which enable and disable registry reflection for 32-bit processes running on 64-bit systems. (<a class="reference external" href="https://bugs.python.org/issue1753245">bpo-1753245</a>)</p> </li> <li><p class="first">The <a class="reference internal" href="../library/msilib.html#module-msilib" title="msilib: Creation of Microsoft Installer files, and CAB files. (Windows)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">msilib</span></code></a> module’s <code class="xref py py-class docutils literal notranslate"><span class="pre">Record</span></code> object gained <code class="xref py py-meth docutils literal notranslate"><span class="pre">GetInteger()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">GetString()</span></code> methods that return field values as an integer or a string. (Contributed by Floris Bruynooghe; <a class="reference external" href="https://bugs.python.org/issue2125">bpo-2125</a>.)</p> </li> </ul> </div> <div class="section" id="port-specific-changes-mac-os-x"> <h3>Port-Specific Changes: Mac OS X<a class="headerlink" href="#port-specific-changes-mac-os-x" title="Permalink to this headline">¶</a></h3> <ul class="simple"> <li>When compiling a framework build of Python, you can now specify the framework name to be used by providing the <code class="xref std std-option docutils literal notranslate"><span class="pre">--with-framework-name=</span></code> option to the <strong class="program">configure</strong> script.</li> <li>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">macfs</span></code> module has been removed. This in turn required the <code class="xref py py-func docutils literal notranslate"><span class="pre">macostools.touched()</span></code> function to be removed because it depended on the <code class="xref py py-mod docutils literal notranslate"><span class="pre">macfs</span></code> module. (<a class="reference external" href="https://bugs.python.org/issue1490190">bpo-1490190</a>)</li> <li>Many other Mac OS modules have been deprecated and will be removed in Python 3.0: <code class="xref py py-mod docutils literal notranslate"><span class="pre">_builtinSuites</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">aepack</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">aetools</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">aetypes</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">applesingle</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">appletrawmain</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">appletrunner</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">argvemulator</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Audio_mac</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">autoGIL</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Carbon</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">cfmfile</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">CodeWarrior</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">ColorPicker</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">EasyDialogs</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Explorer</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Finder</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">FrameWork</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">findertools</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">ic</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">icglue</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">icopen</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">macerrors</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">MacOS</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">macfs</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">macostools</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">macresource</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">MiniAEFrame</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Nav</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Netscape</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">OSATerminology</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">pimp</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">PixMapWrapper</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">StdSuites</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">SystemEvents</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">Terminal</span></code>, and <code class="xref py py-mod docutils literal notranslate"><span class="pre">terminalcommand</span></code>.</li> </ul> </div> <div class="section" id="port-specific-changes-irix"> <h3>Port-Specific Changes: IRIX<a class="headerlink" href="#port-specific-changes-irix" title="Permalink to this headline">¶</a></h3> <p>A number of old IRIX-specific modules were deprecated and will be removed in Python 3.0: <code class="xref py py-mod docutils literal notranslate"><span class="pre">al</span></code> and <code class="xref py py-mod docutils literal notranslate"><span class="pre">AL</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">cd</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">cddb</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">cdplayer</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">CL</span></code> and <code class="xref py py-mod docutils literal notranslate"><span class="pre">cl</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">DEVICE</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">ERRNO</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">FILE</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">FL</span></code> and <code class="xref py py-mod docutils literal notranslate"><span class="pre">fl</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">flp</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">fm</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">GET</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">GLWS</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">GL</span></code> and <code class="xref py py-mod docutils literal notranslate"><span class="pre">gl</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">IN</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">IOCTL</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">jpeg</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">panelparser</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">readcd</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">SV</span></code> and <code class="xref py py-mod docutils literal notranslate"><span class="pre">sv</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">torgb</span></code>, <code class="xref py py-mod docutils literal notranslate"><span class="pre">videoreader</span></code>, and <code class="xref py py-mod docutils literal notranslate"><span class="pre">WAIT</span></code>.</p> </div> </div> <div class="section" id="porting-to-python-2-6"> <h2>Porting to Python 2.6<a class="headerlink" href="#porting-to-python-2-6" title="Permalink to this headline">¶</a></h2> <p>This section lists previously described changes and other bugfixes that may require changes to your code:</p> <ul> <li><p class="first">Classes that aren’t supposed to be hashable should set <code class="docutils literal notranslate"><span class="pre">__hash__</span> <span class="pre">=</span> <span class="pre">None</span></code> in their definitions to indicate the fact.</p> </li> <li><p class="first">String exceptions have been removed. Attempting to use them raises a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p> </li> <li><p class="first">The <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__init__()</span></code></a> method of <a class="reference internal" href="../library/collections.html#collections.deque" title="collections.deque"><code class="xref py py-class docutils literal notranslate"><span class="pre">collections.deque</span></code></a> now clears any existing contents of the deque before adding elements from the iterable. This change makes the behavior match <code class="docutils literal notranslate"><span class="pre">list.__init__()</span></code>.</p> </li> <li><p class="first"><a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">object.__init__()</span></code></a> previously accepted arbitrary arguments and keyword arguments, ignoring them. In Python 2.6, this is no longer allowed and will result in a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>. This will affect <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__init__()</span></code></a> methods that end up calling the corresponding method on <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></a> (perhaps through using <a class="reference internal" href="../library/functions.html#super" title="super"><code class="xref py py-func docutils literal notranslate"><span class="pre">super()</span></code></a>). See <a class="reference external" href="https://bugs.python.org/issue1683368">bpo-1683368</a> for discussion.</p> </li> <li><p class="first">The <code class="xref py py-class docutils literal notranslate"><span class="pre">Decimal</span></code> constructor now accepts leading and trailing whitespace when passed a string. Previously it would raise an <code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidOperation</span></code> exception. On the other hand, the <code class="xref py py-meth docutils literal notranslate"><span class="pre">create_decimal()</span></code> method of <code class="xref py py-class docutils literal notranslate"><span class="pre">Context</span></code> objects now explicitly disallows extra whitespace, raising a <code class="xref py py-exc docutils literal notranslate"><span class="pre">ConversionSyntax</span></code> exception.</p> </li> <li><p class="first">Due to an implementation accident, if you passed a file path to the built-in <a class="reference internal" href="../library/functions.html#__import__" title="__import__"><code class="xref py py-func docutils literal notranslate"><span class="pre">__import__()</span></code></a> function, it would actually import the specified file. This was never intended to work, however, and the implementation now explicitly checks for this case and raises an <a class="reference internal" href="../library/exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ImportError</span></code></a>.</p> </li> <li><p class="first">C API: the <a class="reference internal" href="../c-api/import.html#c.PyImport_Import" title="PyImport_Import"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyImport_Import()</span></code></a> and <a class="reference internal" href="../c-api/import.html#c.PyImport_ImportModule" title="PyImport_ImportModule"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyImport_ImportModule()</span></code></a> functions now default to absolute imports, not relative imports. This will affect C extensions that import other modules.</p> </li> <li><p class="first">C API: extension data types that shouldn’t be hashable should define their <code class="docutils literal notranslate"><span class="pre">tp_hash</span></code> slot to <a class="reference internal" href="../c-api/object.html#c.PyObject_HashNotImplemented" title="PyObject_HashNotImplemented"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_HashNotImplemented()</span></code></a>.</p> </li> <li><p class="first">The <a class="reference internal" href="../library/socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> module exception <a class="reference internal" href="../library/socket.html#socket.error" title="socket.error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">socket.error</span></code></a> now inherits from <a class="reference internal" href="../library/exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a>. Previously it wasn’t a subclass of <code class="xref py py-exc docutils literal notranslate"><span class="pre">StandardError</span></code> but now it is, through <a class="reference internal" href="../library/exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a>. (Implemented by Gregory P. Smith; <a class="reference external" href="https://bugs.python.org/issue1706815">bpo-1706815</a>.)</p> </li> <li><p class="first">The <code class="xref py py-mod docutils literal notranslate"><span class="pre">xmlrpclib</span></code> module no longer automatically converts <a class="reference internal" href="../library/datetime.html#datetime.date" title="datetime.date"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime.date</span></code></a> and <a class="reference internal" href="../library/datetime.html#datetime.time" title="datetime.time"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime.time</span></code></a> to the <code class="xref py py-class docutils literal notranslate"><span class="pre">xmlrpclib.DateTime</span></code> type; the conversion semantics were not necessarily correct for all applications. Code using <code class="xref py py-mod docutils literal notranslate"><span class="pre">xmlrpclib</span></code> should convert <code class="xref py py-class docutils literal notranslate"><span class="pre">date</span></code> and <a class="reference internal" href="../library/datetime.html#datetime.time" title="datetime.time"><code class="xref py py-class docutils literal notranslate"><span class="pre">time</span></code></a> instances. (<a class="reference external" href="https://bugs.python.org/issue1330538">bpo-1330538</a>)</p> </li> <li><p class="first">(3.0-warning mode) The <a class="reference internal" href="../library/exceptions.html#Exception" title="Exception"><code class="xref py py-class docutils literal notranslate"><span class="pre">Exception</span></code></a> class now warns when accessed using slicing or index access; having <a class="reference internal" href="../library/exceptions.html#Exception" title="Exception"><code class="xref py py-class docutils literal notranslate"><span class="pre">Exception</span></code></a> behave like a tuple is being phased out.</p> </li> <li><p class="first">(3.0-warning mode) inequality comparisons between two dictionaries or two objects that don’t implement comparison methods are reported as warnings. <code class="docutils literal notranslate"><span class="pre">dict1</span> <span class="pre">==</span> <span class="pre">dict2</span></code> still works, but <code class="docutils literal notranslate"><span class="pre">dict1</span> <span class="pre"><</span> <span class="pre">dict2</span></code> is being phased out.</p> <p>Comparisons between cells, which are an implementation detail of Python’s scoping rules, also cause warnings because such comparisons are forbidden entirely in 3.0.</p> </li> </ul> </div> <div class="section" id="acknowledgements"> <span id="acks"></span><h2>Acknowledgements<a class="headerlink" href="#acknowledgements" title="Permalink to this headline">¶</a></h2> <p>The author would like to thank the following people for offering suggestions, corrections and assistance with various drafts of this article: Georg Brandl, Steve Brown, Nick Coghlan, Ralph Corderoy, Jim Jewett, Kent Johnson, Chris Lambacher, Martin Michlmayr, Antoine Pitrou, Brian Warner.</p> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">What’s New in Python 2.6</a><ul> <li><a class="reference internal" href="#python-3-0">Python 3.0</a></li> <li><a class="reference internal" href="#changes-to-the-development-process">Changes to the Development Process</a><ul> <li><a class="reference internal" href="#new-issue-tracker-roundup">New Issue Tracker: Roundup</a></li> <li><a class="reference internal" href="#new-documentation-format-restructuredtext-using-sphinx">New Documentation Format: reStructuredText Using Sphinx</a></li> </ul> </li> <li><a class="reference internal" href="#pep-343-the-with-statement">PEP 343: The ‘with’ statement</a><ul> <li><a class="reference internal" href="#writing-context-managers">Writing Context Managers</a></li> <li><a class="reference internal" href="#the-contextlib-module">The contextlib module</a></li> </ul> </li> <li><a class="reference internal" href="#pep-366-explicit-relative-imports-from-a-main-module">PEP 366: Explicit Relative Imports From a Main Module</a></li> <li><a class="reference internal" href="#pep-370-per-user-site-packages-directory">PEP 370: Per-user <code class="docutils literal notranslate"><span class="pre">site-packages</span></code> Directory</a></li> <li><a class="reference internal" href="#pep-371-the-multiprocessing-package">PEP 371: The <code class="docutils literal notranslate"><span class="pre">multiprocessing</span></code> Package</a></li> <li><a class="reference internal" href="#pep-3101-advanced-string-formatting">PEP 3101: Advanced String Formatting</a></li> <li><a class="reference internal" href="#pep-3105-print-as-a-function">PEP 3105: <code class="docutils literal notranslate"><span class="pre">print</span></code> As a Function</a></li> <li><a class="reference internal" href="#pep-3110-exception-handling-changes">PEP 3110: Exception-Handling Changes</a></li> <li><a class="reference internal" href="#pep-3112-byte-literals">PEP 3112: Byte Literals</a></li> <li><a class="reference internal" href="#pep-3116-new-i-o-library">PEP 3116: New I/O Library</a></li> <li><a class="reference internal" href="#pep-3118-revised-buffer-protocol">PEP 3118: Revised Buffer Protocol</a></li> <li><a class="reference internal" href="#pep-3119-abstract-base-classes">PEP 3119: Abstract Base Classes</a></li> <li><a class="reference internal" href="#pep-3127-integer-literal-support-and-syntax">PEP 3127: Integer Literal Support and Syntax</a></li> <li><a class="reference internal" href="#pep-3129-class-decorators">PEP 3129: Class Decorators</a></li> <li><a class="reference internal" href="#pep-3141-a-type-hierarchy-for-numbers">PEP 3141: A Type Hierarchy for Numbers</a><ul> <li><a class="reference internal" href="#the-fractions-module">The <code class="docutils literal notranslate"><span class="pre">fractions</span></code> Module</a></li> </ul> </li> <li><a class="reference internal" href="#other-language-changes">Other Language Changes</a><ul> <li><a class="reference internal" href="#optimizations">Optimizations</a></li> <li><a class="reference internal" href="#interpreter-changes">Interpreter Changes</a></li> </ul> </li> <li><a class="reference internal" href="#new-and-improved-modules">New and Improved Modules</a><ul> <li><a class="reference internal" href="#the-ast-module">The <code class="docutils literal notranslate"><span class="pre">ast</span></code> module</a></li> <li><a class="reference internal" href="#the-future-builtins-module">The <code class="docutils literal notranslate"><span class="pre">future_builtins</span></code> module</a></li> <li><a class="reference internal" href="#the-json-module-javascript-object-notation">The <code class="docutils literal notranslate"><span class="pre">json</span></code> module: JavaScript Object Notation</a></li> <li><a class="reference internal" href="#the-plistlib-module-a-property-list-parser">The <code class="docutils literal notranslate"><span class="pre">plistlib</span></code> module: A Property-List Parser</a></li> <li><a class="reference internal" href="#ctypes-enhancements">ctypes Enhancements</a></li> <li><a class="reference internal" href="#improved-ssl-support">Improved SSL Support</a></li> </ul> </li> <li><a class="reference internal" href="#deprecations-and-removals">Deprecations and Removals</a></li> <li><a class="reference internal" href="#build-and-c-api-changes">Build and C API Changes</a><ul> <li><a class="reference internal" href="#port-specific-changes-windows">Port-Specific Changes: Windows</a></li> <li><a class="reference internal" href="#port-specific-changes-mac-os-x">Port-Specific Changes: Mac OS X</a></li> <li><a class="reference internal" href="#port-specific-changes-irix">Port-Specific Changes: IRIX</a></li> </ul> </li> <li><a class="reference internal" href="#porting-to-python-2-6">Porting to Python 2.6</a></li> <li><a class="reference internal" href="#acknowledgements">Acknowledgements</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="2.7.html" title="previous chapter">What’s New in Python 2.7</a></p> <h4>Next topic</h4> <p class="topless"><a href="2.5.html" title="next chapter">What’s New in Python 2.5</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.6/Doc/whatsnew/2.6.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="2.5.html" title="What’s New in Python 2.5" 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