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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>15. Appendix — Python 2.7.16 documentation</title> <link rel="stylesheet" href="../_static/classic.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 2.7.16 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="Python Setup and Usage" href="../using/index.html" /> <link rel="prev" title="14. Floating Point Arithmetic: Issues and Limitations" href="floatingpoint.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/2/tutorial/appendix.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="../using/index.html" title="Python Setup and Usage" accesskey="N">next</a> |</li> <li class="right" > <a href="floatingpoint.html" title="14. Floating Point Arithmetic: Issues and Limitations" 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">Python 2.7.16 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">The Python Tutorial</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="appendix"> <span id="tut-appendix"></span><h1>15. Appendix<a class="headerlink" href="#appendix" title="Permalink to this headline">¶</a></h1> <div class="section" id="interactive-mode"> <span id="tut-interac"></span><h2>15.1. Interactive Mode<a class="headerlink" href="#interactive-mode" title="Permalink to this headline">¶</a></h2> <div class="section" id="error-handling"> <span id="tut-error"></span><h3>15.1.1. Error Handling<a class="headerlink" href="#error-handling" title="Permalink to this headline">¶</a></h3> <p>When an error occurs, the interpreter prints an error message and a stack trace. In interactive mode, it then returns to the primary prompt; when input came from a file, it exits with a nonzero exit status after printing the stack trace. (Exceptions handled by an <a class="reference internal" href="../reference/compound_stmts.html#except"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">except</span></code></a> clause in a <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> statement are not errors in this context.) Some errors are unconditionally fatal and cause an exit with a nonzero exit; this applies to internal inconsistencies and some cases of running out of memory. All error messages are written to the standard error stream; normal output from executed commands is written to standard output.</p> <p>Typing the interrupt character (usually <kbd class="kbd docutils literal notranslate">Control-C</kbd> or <kbd class="kbd docutils literal notranslate">Delete</kbd>) to the primary or secondary prompt cancels the input and returns to the primary prompt. <a class="footnote-reference" href="#id2" id="id1">[1]</a> Typing an interrupt while a command is executing raises the <a class="reference internal" href="../library/exceptions.html#exceptions.KeyboardInterrupt" title="exceptions.KeyboardInterrupt"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyboardInterrupt</span></code></a> exception, which may be handled by a <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> statement.</p> </div> <div class="section" id="executable-python-scripts"> <span id="tut-scripts"></span><h3>15.1.2. Executable Python Scripts<a class="headerlink" href="#executable-python-scripts" title="Permalink to this headline">¶</a></h3> <p>On BSD’ish Unix systems, Python scripts can be made directly executable, like shell scripts, by putting the line</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python</span> </pre></div> </div> <p>(assuming that the interpreter is on the user’s <span class="target" id="index-0"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code>) at the beginning of the script and giving the file an executable mode. The <code class="docutils literal notranslate"><span class="pre">#!</span></code> must be the first two characters of the file. On some platforms, this first line must end with a Unix-style line ending (<code class="docutils literal notranslate"><span class="pre">'\n'</span></code>), not a Windows (<code class="docutils literal notranslate"><span class="pre">'\r\n'</span></code>) line ending. Note that the hash, or pound, character, <code class="docutils literal notranslate"><span class="pre">'#'</span></code>, is used to start a comment in Python.</p> <p>The script can be given an executable mode, or permission, using the <strong class="program">chmod</strong> command.</p> <div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>$ chmod +x myscript.py </pre></div> </div> <p>On Windows systems, there is no notion of an “executable mode”. The Python installer automatically associates <code class="docutils literal notranslate"><span class="pre">.py</span></code> files with <code class="docutils literal notranslate"><span class="pre">python.exe</span></code> so that a double-click on a Python file will run it as a script. The extension can also be <code class="docutils literal notranslate"><span class="pre">.pyw</span></code>, in that case, the console window that normally appears is suppressed.</p> </div> <div class="section" id="the-interactive-startup-file"> <span id="tut-startup"></span><h3>15.1.3. The Interactive Startup File<a class="headerlink" href="#the-interactive-startup-file" title="Permalink to this headline">¶</a></h3> <p>When you use Python interactively, it is frequently handy to have some standard commands executed every time the interpreter is started. You can do this by setting an environment variable named <span class="target" id="index-1"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONSTARTUP"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONSTARTUP</span></code></a> to the name of a file containing your start-up commands. This is similar to the <code class="file docutils literal notranslate"><span class="pre">.profile</span></code> feature of the Unix shells.</p> <p>This file is only read in interactive sessions, not when Python reads commands from a script, and not when <code class="file docutils literal notranslate"><span class="pre">/dev/tty</span></code> is given as the explicit source of commands (which otherwise behaves like an interactive session). It is executed in the same namespace where interactive commands are executed, so that objects that it defines or imports can be used without qualification in the interactive session. You can also change the prompts <code class="docutils literal notranslate"><span class="pre">sys.ps1</span></code> and <code class="docutils literal notranslate"><span class="pre">sys.ps2</span></code> in this file.</p> <p>If you want to read an additional start-up file from the current directory, you can program this in the global start-up file using code like <code class="docutils literal notranslate"><span class="pre">if</span> <span class="pre">os.path.isfile('.pythonrc.py'):</span> <span class="pre">exec(open('.pythonrc.py').read())</span></code>. If you want to use the startup file in a script, you must do this explicitly in the script:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">os</span> <span class="n">filename</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s1">'PYTHONSTARTUP'</span><span class="p">)</span> <span class="k">if</span> <span class="n">filename</span> <span class="ow">and</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">isfile</span><span class="p">(</span><span class="n">filename</span><span class="p">):</span> <span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span> <span class="k">as</span> <span class="n">fobj</span><span class="p">:</span> <span class="n">startup_file</span> <span class="o">=</span> <span class="n">fobj</span><span class="o">.</span><span class="n">read</span><span class="p">()</span> <span class="n">exec</span><span class="p">(</span><span class="n">startup_file</span><span class="p">)</span> </pre></div> </div> </div> <div class="section" id="the-customization-modules"> <span id="tut-customize"></span><h3>15.1.4. The Customization Modules<a class="headerlink" href="#the-customization-modules" title="Permalink to this headline">¶</a></h3> <p>Python provides two hooks to let you customize it: <code class="xref py py-mod docutils literal notranslate"><span class="pre">sitecustomize</span></code> and <code class="xref py py-mod docutils literal notranslate"><span class="pre">usercustomize</span></code>. To see how it works, you need first to find the location of your user site-packages directory. Start Python and run this code:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">site</span> <span class="gp">>>> </span><span class="n">site</span><span class="o">.</span><span class="n">getusersitepackages</span><span class="p">()</span> <span class="go">'/home/user/.local/lib/python2.7/site-packages'</span> </pre></div> </div> <p>Now you can create a file named <code class="file docutils literal notranslate"><span class="pre">usercustomize.py</span></code> in that directory and put anything you want in it. It will affect every invocation of Python, unless it is started 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 to disable the automatic import.</p> <p><code class="xref py py-mod docutils literal notranslate"><span class="pre">sitecustomize</span></code> works in the same way, but is typically created by an administrator of the computer in the global site-packages directory, and is imported before <code class="xref py py-mod docutils literal notranslate"><span class="pre">usercustomize</span></code>. See the documentation of the <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate"><span class="pre">site</span></code></a> module for more details.</p> <p class="rubric">Footnotes</p> <table class="docutils footnote" frame="void" id="id2" rules="none"> <colgroup><col class="label" /><col /></colgroup> <tbody valign="top"> <tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>A problem with the GNU Readline package may prevent this.</td></tr> </tbody> </table> </div> </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="#">15. Appendix</a><ul> <li><a class="reference internal" href="#interactive-mode">15.1. Interactive Mode</a><ul> <li><a class="reference internal" href="#error-handling">15.1.1. Error Handling</a></li> <li><a class="reference internal" href="#executable-python-scripts">15.1.2. Executable Python Scripts</a></li> <li><a class="reference internal" href="#the-interactive-startup-file">15.1.3. The Interactive Startup File</a></li> <li><a class="reference internal" href="#the-customization-modules">15.1.4. The Customization Modules</a></li> </ul> </li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="floatingpoint.html" title="previous chapter">14. Floating Point Arithmetic: Issues and Limitations</a></p> <h4>Next topic</h4> <p class="topless"><a href="../using/index.html" title="next chapter">Python Setup and Usage</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/tutorial/appendix.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search.html" method="get"> <input 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> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </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="../using/index.html" title="Python Setup and Usage" >next</a> |</li> <li class="right" > <a href="floatingpoint.html" title="14. 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