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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 2.7.18 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/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 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="file:///usr/share/doc/python2.7/html/tutorial/interpreter.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/tutorial/interpreter.html"> Python documentation for the Python3 version packaged in this release</a>. </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" 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">Python 2.7.18 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="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/python</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-default notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> </pre></div> </div> <p>to the shell. 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:\Python27</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-default 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">python27</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 usually aren’t very sophisticated. On Unix, whoever installed the interpreter may have enabled support for the GNU readline library, which adds more elaborate interactive editing and history features. 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="go">python</span> <span class="go">Python 2.7 (#1, Feb 28 2010, 00:02:06)</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-default 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="mi">1</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="s2">"Be careful not to fall off!"</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 ASCII. 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-default 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-default 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-default notranslate"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python</span> <span class="c1"># -*- coding: cp1252 -*-</span> </pre></div> </div> </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. 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