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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>2. Using the Python Interpreter — 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="3. An Informal Introduction to Python" href="introduction.html" /> <link rel="prev" title="1. Whetting Your Appetite" href="appetite.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/tutorial/interpreter.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="introduction.html" title="3. An Informal Introduction to Python" accesskey="N">next</a> |</li> <li class="right" > <a href="appetite.html" title="1. Whetting Your Appetite" 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">The Python Tutorial</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="using-the-python-interpreter"> <span id="tut-using"></span><h1>2. Using the Python Interpreter<a class="headerlink" href="#using-the-python-interpreter" title="Permalink to this headline">¶</a></h1> <div class="section" id="invoking-the-interpreter"> <span id="tut-invoking"></span><h2>2.1. Invoking the Interpreter<a class="headerlink" href="#invoking-the-interpreter" title="Permalink to this headline">¶</a></h2> <p>The Python interpreter is usually installed as <code class="file docutils literal notranslate"><span class="pre">/usr/local/bin/python3.6</span></code> on those machines where it is available; putting <code class="file docutils literal notranslate"><span class="pre">/usr/local/bin</span></code> in your Unix shell’s search path makes it possible to start it by typing the command:</p> <div class="highlight-text notranslate"><div class="highlight"><pre><span></span>python3.6 </pre></div> </div> <p>to the shell. <a class="footnote-reference" href="#id2" id="id1">[1]</a> Since the choice of the directory where the interpreter lives is an installation option, other places are possible; check with your local Python guru or system administrator. (E.g., <code class="file docutils literal notranslate"><span class="pre">/usr/local/python</span></code> is a popular alternative location.)</p> <p>On Windows machines, the Python installation is usually placed in <code class="file docutils literal notranslate"><span class="pre">C:\Python36</span></code>, though you can change this when you’re running the installer. To add this directory to your path, you can type the following command into the command prompt in a DOS box:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="nb">set</span> <span class="n">path</span><span class="o">=%</span><span class="n">path</span><span class="o">%</span><span class="p">;</span><span class="n">C</span><span class="p">:</span>\<span class="n">python36</span> </pre></div> </div> <p>Typing an end-of-file character (<kbd class="kbd docutils literal notranslate">Control-D</kbd> on Unix, <kbd class="kbd docutils literal notranslate">Control-Z</kbd> on Windows) at the primary prompt causes the interpreter to exit with a zero exit status. If that doesn’t work, you can exit the interpreter by typing the following command: <code class="docutils literal notranslate"><span class="pre">quit()</span></code>.</p> <p>The interpreter’s line-editing features include interactive editing, history substitution and code completion on systems that support readline. Perhaps the quickest check to see whether command line editing is supported is typing <kbd class="kbd docutils literal notranslate">Control-P</kbd> to the first Python prompt you get. If it beeps, you have command line editing; see Appendix <a class="reference internal" href="interactive.html#tut-interacting"><span class="std std-ref">Interactive Input Editing and History Substitution</span></a> for an introduction to the keys. If nothing appears to happen, or if <code class="docutils literal notranslate"><span class="pre">^P</span></code> is echoed, command line editing isn’t available; you’ll only be able to use backspace to remove characters from the current line.</p> <p>The interpreter operates somewhat like the Unix shell: when called with standard input connected to a tty device, it reads and executes commands interactively; when called with a file name argument or with a file as standard input, it reads and executes a <em>script</em> from that file.</p> <p>A second way of starting the interpreter is <code class="docutils literal notranslate"><span class="pre">python</span> <span class="pre">-c</span> <span class="pre">command</span> <span class="pre">[arg]</span> <span class="pre">...</span></code>, which executes the statement(s) in <em>command</em>, analogous to the shell’s <a class="reference internal" href="../using/cmdline.html#cmdoption-c"><code class="xref std std-option docutils literal notranslate"><span class="pre">-c</span></code></a> option. Since Python statements often contain spaces or other characters that are special to the shell, it is usually advised to quote <em>command</em> in its entirety with single quotes.</p> <p>Some Python modules are also useful as scripts. These can be invoked using <code class="docutils literal notranslate"><span class="pre">python</span> <span class="pre">-m</span> <span class="pre">module</span> <span class="pre">[arg]</span> <span class="pre">...</span></code>, which executes the source file for <em>module</em> as if you had spelled out its full name on the command line.</p> <p>When a script file is used, it is sometimes useful to be able to run the script and enter interactive mode afterwards. This can be done by passing <a class="reference internal" href="../using/cmdline.html#cmdoption-i"><code class="xref std std-option docutils literal notranslate"><span class="pre">-i</span></code></a> before the script.</p> <p>All command line options are described in <a class="reference internal" href="../using/cmdline.html#using-on-general"><span class="std std-ref">Command line and environment</span></a>.</p> <div class="section" id="argument-passing"> <span id="tut-argpassing"></span><h3>2.1.1. Argument Passing<a class="headerlink" href="#argument-passing" title="Permalink to this headline">¶</a></h3> <p>When known to the interpreter, the script name and additional arguments thereafter are turned into a list of strings and assigned to the <code class="docutils literal notranslate"><span class="pre">argv</span></code> variable in the <code class="docutils literal notranslate"><span class="pre">sys</span></code> module. You can access this list by executing <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">sys</span></code>. The length of the list is at least one; when no script and no arguments are given, <code class="docutils literal notranslate"><span class="pre">sys.argv[0]</span></code> is an empty string. When the script name is given as <code class="docutils literal notranslate"><span class="pre">'-'</span></code> (meaning standard input), <code class="docutils literal notranslate"><span class="pre">sys.argv[0]</span></code> is set to <code class="docutils literal notranslate"><span class="pre">'-'</span></code>. When <a class="reference internal" href="../using/cmdline.html#cmdoption-c"><code class="xref std std-option docutils literal notranslate"><span class="pre">-c</span></code></a> <em>command</em> is used, <code class="docutils literal notranslate"><span class="pre">sys.argv[0]</span></code> is set to <code class="docutils literal notranslate"><span class="pre">'-c'</span></code>. When <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> <em>module</em> is used, <code class="docutils literal notranslate"><span class="pre">sys.argv[0]</span></code> is set to the full name of the located module. Options found after <a class="reference internal" href="../using/cmdline.html#cmdoption-c"><code class="xref std std-option docutils literal notranslate"><span class="pre">-c</span></code></a> <em>command</em> or <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> <em>module</em> are not consumed by the Python interpreter’s option processing but left in <code class="docutils literal notranslate"><span class="pre">sys.argv</span></code> for the command or module to handle.</p> </div> <div class="section" id="interactive-mode"> <span id="tut-interactive"></span><h3>2.1.2. Interactive Mode<a class="headerlink" href="#interactive-mode" title="Permalink to this headline">¶</a></h3> <p>When commands are read from a tty, the interpreter is said to be in <em>interactive mode</em>. In this mode it prompts for the next command with the <em>primary prompt</em>, usually three greater-than signs (<code class="docutils literal notranslate"><span class="pre">>>></span></code>); for continuation lines it prompts with the <em>secondary prompt</em>, by default three dots (<code class="docutils literal notranslate"><span class="pre">...</span></code>). The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt:</p> <div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$</span> python3.6 <span class="go">Python 3.6 (default, Sep 16 2015, 09:25:04)</span> <span class="go">[GCC 4.8.2] on linux</span> <span class="go">Type "help", "copyright", "credits" or "license" for more information.</span> <span class="gp">></span>>> </pre></div> </div> <p>Continuation lines are needed when entering a multi-line construct. As an example, take a look at this <a class="reference internal" href="../reference/compound_stmts.html#if"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">if</span></code></a> statement:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">the_world_is_flat</span> <span class="o">=</span> <span class="kc">True</span> <span class="gp">>>> </span><span class="k">if</span> <span class="n">the_world_is_flat</span><span class="p">:</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Be careful not to fall off!"</span><span class="p">)</span> <span class="gp">...</span> <span class="go">Be careful not to fall off!</span> </pre></div> </div> <p>For more on interactive mode, see <a class="reference internal" href="appendix.html#tut-interac"><span class="std std-ref">Interactive Mode</span></a>.</p> </div> </div> <div class="section" id="the-interpreter-and-its-environment"> <span id="tut-interp"></span><h2>2.2. The Interpreter and Its Environment<a class="headerlink" href="#the-interpreter-and-its-environment" title="Permalink to this headline">¶</a></h2> <div class="section" id="source-code-encoding"> <span id="tut-source-encoding"></span><h3>2.2.1. Source Code Encoding<a class="headerlink" href="#source-code-encoding" title="Permalink to this headline">¶</a></h3> <p>By default, Python source files are treated as encoded in UTF-8. In that encoding, characters of most languages in the world can be used simultaneously in string literals, identifiers and comments — although the standard library only uses ASCII characters for identifiers, a convention that any portable code should follow. To display all these characters properly, your editor must recognize that the file is UTF-8, and it must use a font that supports all the characters in the file.</p> <p>To declare an encoding other than the default one, a special comment line should be added as the <em>first</em> line of the file. The syntax is as follows:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># -*- coding: encoding -*-</span> </pre></div> </div> <p>where <em>encoding</em> is one of the valid <a class="reference internal" href="../library/codecs.html#module-codecs" title="codecs: Encode and decode data and streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">codecs</span></code></a> supported by Python.</p> <p>For example, to declare that Windows-1252 encoding is to be used, the first line of your source code file should be:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># -*- coding: cp1252 -*-</span> </pre></div> </div> <p>One exception to the <em>first line</em> rule is when the source code starts with a <a class="reference internal" href="appendix.html#tut-scripts"><span class="std std-ref">UNIX “shebang” line</span></a>. In this case, the encoding declaration should be added as the second line of the file. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python3</span> <span class="c1"># -*- coding: cp1252 -*-</span> </pre></div> </div> <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>On Unix, the Python 3.x interpreter is by default not installed with the executable named <code class="docutils literal notranslate"><span class="pre">python</span></code>, so that it does not conflict with a simultaneously installed Python 2.x executable.</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="#">2. Using the Python Interpreter</a><ul> <li><a class="reference internal" href="#invoking-the-interpreter">2.1. Invoking the Interpreter</a><ul> <li><a class="reference internal" href="#argument-passing">2.1.1. Argument Passing</a></li> <li><a class="reference internal" href="#interactive-mode">2.1.2. Interactive Mode</a></li> </ul> </li> <li><a class="reference internal" href="#the-interpreter-and-its-environment">2.2. The Interpreter and Its Environment</a><ul> <li><a class="reference internal" href="#source-code-encoding">2.2.1. Source Code Encoding</a></li> </ul> </li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="appetite.html" title="previous chapter">1. Whetting Your Appetite</a></p> <h4>Next topic</h4> <p class="topless"><a href="introduction.html" title="next chapter">3. An Informal Introduction to Python</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/tutorial/interpreter.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="introduction.html" title="3. An Informal Introduction to Python" >next</a> |</li> <li class="right" > <a href="appetite.html" title="1. 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