<!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="Content-Type" content="text/html; charset=utf-8" />
<title>29.4. __main__ — Top-level script environment — Python 3.5.3 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">
var DOCUMENTATION_OPTIONS = {
URL_ROOT: '../',
VERSION: '3.5.3',
COLLAPSE_INDEX: false,
FILE_SUFFIX: '.html',
HAS_SOURCE: true
};
</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 3.5.3 documentation"
href="../_static/opensearch.xml"/>
<link rel="author" title="About these documents" href="../about.html" />
<link rel="copyright" title="Copyright" href="../copyright.html" />
<link rel="top" title="Python 3.5.3 documentation" href="../contents.html" />
<link rel="up" title="29. Python Runtime Services" href="python.html" />
<link rel="next" title="29.5. warnings — Warning control" href="warnings.html" />
<link rel="prev" title="29.3. builtins — Built-in objects" href="builtins.html" />
<link rel="shortcut icon" type="image/png" href="../_static/py.png" />
<script type="text/javascript" src="../_static/copybutton.js"></script>
<script type="text/javascript" src="../_static/version_switch.js"></script>
</head>
<body role="document">
<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="warnings.html" title="29.5. warnings — Warning control"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="builtins.html" title="29.3. builtins — Built-in objects"
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>
<span class="version_switcher_placeholder">3.5.3</span>
<a href="../index.html">Documentation </a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li>
<li class="nav-item nav-item-2"><a href="python.html" accesskey="U">29. Python Runtime Services</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="module-__main__">
<span id="main-top-level-script-environment"></span><h1>29.4. <a class="reference internal" href="#module-__main__" title="__main__: The environment where the top-level script is run."><code class="xref py py-mod docutils literal"><span class="pre">__main__</span></code></a> — Top-level script environment<a class="headerlink" href="#module-__main__" title="Permalink to this headline">¶</a></h1>
<hr class="docutils" />
<p><code class="docutils literal"><span class="pre">'__main__'</span></code> is the name of the scope in which top-level code executes.
A module’s __name__ is set equal to <code class="docutils literal"><span class="pre">'__main__'</span></code> when read from
standard input, a script, or from an interactive prompt.</p>
<p>A module can discover whether or not it is running in the main scope by
checking its own <code class="docutils literal"><span class="pre">__name__</span></code>, which allows a common idiom for conditionally
executing code in a module when it is run as a script or with <code class="docutils literal"><span class="pre">python</span>
<span class="pre">-m</span></code> but not when it is imported:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s2">"__main__"</span><span class="p">:</span>
<span class="c1"># execute only if run as a script</span>
<span class="n">main</span><span class="p">()</span>
</pre></div>
</div>
<p>For a package, the same effect can be achieved by including a
<code class="docutils literal"><span class="pre">__main__.py</span></code> module, the contents of which will be executed when the
module is run with <code class="docutils literal"><span class="pre">-m</span></code>.</p>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h4>Previous topic</h4>
<p class="topless"><a href="builtins.html"
title="previous chapter">29.3. <code class="docutils literal"><span class="pre">builtins</span></code> — Built-in objects</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="warnings.html"
title="next chapter">29.5. <code class="docutils literal"><span class="pre">warnings</span></code> — Warning control</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="../_sources/library/__main__.txt"
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="warnings.html" title="29.5. warnings — Warning control"
>next</a> |</li>
<li class="right" >
<a href="builtins.html" title="29.3. builtins — Built-in objects"
>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>
<span class="version_switcher_placeholder">3.5.3</span>
<a href="../index.html">Documentation </a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li>
<li class="nav-item nav-item-2"><a href="python.html" >29. Python Runtime Services</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="footer">
© <a href="../copyright.html">Copyright</a> 2001-2017, Python Software Foundation.
<br />
The Python Software Foundation is a non-profit corporation.
<a href="https://www.python.org/psf/donations/">Please donate.</a>
<br />
Last updated on Jan 20, 2017.
<a href="../bugs.html">Found a bug</a>?
<br />
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.3.3.
</div>
</body>
</html>
