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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>28.9. atexit — Exit handlers — 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="28.10. traceback — Print or retrieve a stack traceback" href="traceback.html" /> <link rel="prev" title="28.8. abc — Abstract Base Classes" href="abc.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/atexit.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div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"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/library/atexit.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="traceback.html" title="28.10. traceback — Print or retrieve a stack traceback" accesskey="N">next</a> |</li> <li class="right" > <a href="abc.html" title="28.8. abc — Abstract Base Classes" 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" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="python.html" accesskey="U">28. Python Runtime Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-atexit"> <span id="atexit-exit-handlers"></span><h1>28.9. <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> — Exit handlers<a class="headerlink" href="#module-atexit" title="Permalink to this headline">¶</a></h1> <div class="versionadded"> <p><span class="versionmodified">New in version 2.0.</span></p> </div> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/2.7/Lib/atexit.py">Lib/atexit.py</a></p> <hr class="docutils" /> <p>The <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> module defines a single function to register cleanup functions. Functions thus registered are automatically executed upon normal interpreter termination. <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> runs these functions in the <em>reverse</em> order in which they were registered; if you register <code class="docutils literal notranslate"><span class="pre">A</span></code>, <code class="docutils literal notranslate"><span class="pre">B</span></code>, and <code class="docutils literal notranslate"><span class="pre">C</span></code>, at interpreter termination time they will be run in the order <code class="docutils literal notranslate"><span class="pre">C</span></code>, <code class="docutils literal notranslate"><span class="pre">B</span></code>, <code class="docutils literal notranslate"><span class="pre">A</span></code>.</p> <p><strong>Note:</strong> The functions registered via this module are not called when the program is killed by a signal not handled by Python, when a Python fatal internal error is detected, or when <a class="reference internal" href="os.html#os._exit" title="os._exit"><code class="xref py py-func docutils literal notranslate"><span class="pre">os._exit()</span></code></a> is called.</p> <p id="index-0">This is an alternate interface to the functionality provided by the <a class="reference internal" href="sys.html#sys.exitfunc" title="sys.exitfunc"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exitfunc()</span></code></a> variable.</p> <p>Note: This module is unlikely to work correctly when used with other code that sets <code class="docutils literal notranslate"><span class="pre">sys.exitfunc</span></code>. In particular, other core Python modules are free to use <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> without the programmer’s knowledge. Authors who use <code class="docutils literal notranslate"><span class="pre">sys.exitfunc</span></code> should convert their code to use <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> instead. The simplest way to convert code that sets <code class="docutils literal notranslate"><span class="pre">sys.exitfunc</span></code> is to import <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> and register the function that had been bound to <code class="docutils literal notranslate"><span class="pre">sys.exitfunc</span></code>.</p> <dl class="function"> <dt id="atexit.register"> <code class="descclassname">atexit.</code><code class="descname">register</code><span class="sig-paren">(</span><em>func</em><span class="optional">[</span>, <em>*args</em><span class="optional">[</span>, <em>**kwargs</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#atexit.register" title="Permalink to this definition">¶</a></dt> <dd><p>Register <em>func</em> as a function to be executed at termination. Any optional arguments that are to be passed to <em>func</em> must be passed as arguments to <a class="reference internal" href="#atexit.register" title="atexit.register"><code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code></a>. It is possible to register the same function and arguments more than once.</p> <p>At normal program termination (for instance, if <a class="reference internal" href="sys.html#sys.exit" title="sys.exit"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exit()</span></code></a> is called or the main module’s execution completes), all functions registered are called in last in, first out order. The assumption is that lower level modules will normally be imported before higher level modules and thus must be cleaned up later.</p> <p>If an exception is raised during execution of the exit handlers, a traceback is printed (unless <a class="reference internal" href="exceptions.html#exceptions.SystemExit" title="exceptions.SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> is raised) and the exception information is saved. After all exit handlers have had a chance to run the last exception to be raised is re-raised.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 2.6: </span>This function now returns <em>func</em>, which makes it possible to use it as a decorator.</p> </div> </dd></dl> <div class="admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt>Module <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">readline</span></code></a></dt> <dd>Useful example of <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> to read and write <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">readline</span></code></a> history files.</dd> </dl> </div> <div class="section" id="atexit-example"> <span id="id1"></span><h2>28.9.1. <a class="reference internal" href="#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> Example<a class="headerlink" href="#atexit-example" title="Permalink to this headline">¶</a></h2> <p>The following simple example demonstrates how a module can initialize a counter from a file when it is imported and save the counter’s updated value automatically when the program terminates without relying on the application making an explicit call into this module at termination.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span> <span class="n">_count</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="nb">open</span><span class="p">(</span><span class="s2">"counter"</span><span class="p">)</span><span class="o">.</span><span class="n">read</span><span class="p">())</span> <span class="k">except</span> <span class="ne">IOError</span><span class="p">:</span> <span class="n">_count</span> <span class="o">=</span> <span class="mi">0</span> <span class="k">def</span> <span class="nf">incrcounter</span><span class="p">(</span><span class="n">n</span><span class="p">):</span> <span class="k">global</span> <span class="n">_count</span> <span class="n">_count</span> <span class="o">=</span> <span class="n">_count</span> <span class="o">+</span> <span class="n">n</span> <span class="k">def</span> <span class="nf">savecounter</span><span class="p">():</span> <span class="nb">open</span><span class="p">(</span><span class="s2">"counter"</span><span class="p">,</span> <span class="s2">"w"</span><span class="p">)</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"</span><span class="si">%d</span><span class="s2">"</span> <span class="o">%</span> <span class="n">_count</span><span class="p">)</span> <span class="kn">import</span> <span class="nn">atexit</span> <span class="n">atexit</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">savecounter</span><span class="p">)</span> </pre></div> </div> <p>Positional and keyword arguments may also be passed to <a class="reference internal" href="#atexit.register" title="atexit.register"><code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code></a> to be passed along to the registered function when it is called:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">goodbye</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">adjective</span><span class="p">):</span> <span class="nb">print</span> <span class="s1">'Goodbye, </span><span class="si">%s</span><span class="s1">, it was </span><span class="si">%s</span><span class="s1"> to meet you.'</span> <span class="o">%</span> <span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">adjective</span><span class="p">)</span> <span class="kn">import</span> <span class="nn">atexit</span> <span class="n">atexit</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">goodbye</span><span class="p">,</span> <span class="s1">'Donny'</span><span class="p">,</span> <span class="s1">'nice'</span><span class="p">)</span> <span class="c1"># or:</span> <span class="n">atexit</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">goodbye</span><span class="p">,</span> <span class="n">adjective</span><span class="o">=</span><span class="s1">'nice'</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s1">'Donny'</span><span class="p">)</span> </pre></div> </div> <p>Usage as a <a class="reference internal" href="../glossary.html#term-decorator"><span class="xref std std-term">decorator</span></a>:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">atexit</span> <span class="nd">@atexit</span><span class="o">.</span><span class="n">register</span> <span class="k">def</span> <span class="nf">goodbye</span><span class="p">():</span> <span class="nb">print</span> <span class="s2">"You are now leaving the Python sector."</span> </pre></div> </div> <p>This only works with functions that can be called without arguments.</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="#">28.9. <code class="docutils literal notranslate"><span class="pre">atexit</span></code> — Exit handlers</a><ul> <li><a class="reference internal" href="#atexit-example">28.9.1. <code class="docutils literal notranslate"><span class="pre">atexit</span></code> Example</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="abc.html" title="previous chapter">28.8. <code class="docutils literal notranslate"><span class="pre">abc</span></code> — Abstract Base Classes</a></p> <h4>Next topic</h4> <p class="topless"><a href="traceback.html" title="next chapter">28.10. <code class="docutils literal notranslate"><span class="pre">traceback</span></code> — Print or retrieve a stack traceback</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/library/atexit.rst.txt" 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