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<div class="section" id="module-atexit">
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<span id="atexit-exit-handlers"></span><h1><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>
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<hr class="docutils" />
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<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 functions to register and unregister cleanup
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functions. Functions thus registered are automatically executed upon normal
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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>
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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>,
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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>,
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<code class="docutils literal notranslate"><span class="pre">A</span></code>.</p>
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<p><strong>Note:</strong> The functions registered via this module are not called when the
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program is killed by a signal not handled by Python, when a Python fatal
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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>
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<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.7: </span>When used with C-API subinterpreters, registered functions
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are local to the interpreter they were registered in.</p>
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</div>
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<dl class="function">
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<dt id="atexit.register">
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<code class="descclassname">atexit.</code><code class="descname">register</code><span class="sig-paren">(</span><em>func</em>, <em>*args</em>, <em>**kwargs</em><span class="sig-paren">)</span><a class="headerlink" href="#atexit.register" title="Permalink to this definition">¶</a></dt>
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<dd><p>Register <em>func</em> as a function to be executed at termination. Any optional
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arguments that are to be passed to <em>func</em> must be passed as arguments to
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<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
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more than once.</p>
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<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
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the main module’s execution completes), all functions registered are called in
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last in, first out order. The assumption is that lower level modules will
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normally be imported before higher level modules and thus must be cleaned up
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later.</p>
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<p>If an exception is raised during execution of the exit handlers, a traceback is
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printed (unless <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> is raised) and the exception information is
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saved. After all exit handlers have had a chance to run the last exception to
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be raised is re-raised.</p>
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<p>This function returns <em>func</em>, which makes it possible to use it as a
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decorator.</p>
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</dd></dl>
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<dl class="function">
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<dt id="atexit.unregister">
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<code class="descclassname">atexit.</code><code class="descname">unregister</code><span class="sig-paren">(</span><em>func</em><span class="sig-paren">)</span><a class="headerlink" href="#atexit.unregister" title="Permalink to this definition">¶</a></dt>
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<dd><p>Remove <em>func</em> from the list of functions to be run at interpreter
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shutdown. After calling <a class="reference internal" href="#atexit.unregister" title="atexit.unregister"><code class="xref py py-func docutils literal notranslate"><span class="pre">unregister()</span></code></a>, <em>func</em> is guaranteed not to be
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called when the interpreter shuts down, even if it was registered more than
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once. <a class="reference internal" href="#atexit.unregister" title="atexit.unregister"><code class="xref py py-func docutils literal notranslate"><span class="pre">unregister()</span></code></a> silently does nothing if <em>func</em> was not previously
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registered.</p>
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</dd></dl>
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<div class="admonition seealso">
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<p class="admonition-title">See also</p>
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<dl class="simple">
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<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><p>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
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files.</p>
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</dd>
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</dl>
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</div>
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<div class="section" id="atexit-example">
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<span id="id1"></span><h2><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>
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<p>The following simple example demonstrates how a module can initialize a counter
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from a file when it is imported and save the counter’s updated value
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automatically when the program terminates without relying on the application
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making an explicit call into this module at termination.</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span>
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<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s2">"counterfile"</span><span class="p">)</span> <span class="k">as</span> <span class="n">infile</span><span class="p">:</span>
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<span class="n">_count</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">infile</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
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<span class="k">except</span> <span class="ne">FileNotFoundError</span><span class="p">:</span>
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<span class="n">_count</span> <span class="o">=</span> <span class="mi">0</span>
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<span class="k">def</span> <span class="nf">incrcounter</span><span class="p">(</span><span class="n">n</span><span class="p">):</span>
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<span class="k">global</span> <span class="n">_count</span>
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<span class="n">_count</span> <span class="o">=</span> <span class="n">_count</span> <span class="o">+</span> <span class="n">n</span>
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<span class="k">def</span> <span class="nf">savecounter</span><span class="p">():</span>
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<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s2">"counterfile"</span><span class="p">,</span> <span class="s2">"w"</span><span class="p">)</span> <span class="k">as</span> <span class="n">outfile</span><span class="p">:</span>
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<span class="n">outfile</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>
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<span class="kn">import</span> <span class="nn">atexit</span>
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<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>
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</pre></div>
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</div>
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<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
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passed along to the registered function when it is called:</p>
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<div class="highlight-python3 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>
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<span class="nb">print</span><span class="p">(</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>
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<span class="kn">import</span> <span class="nn">atexit</span>
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<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>
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<span class="c1"># or:</span>
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<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>
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</pre></div>
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</div>
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<p>Usage as a <a class="reference internal" href="../glossary.html#term-decorator"><span class="xref std std-term">decorator</span></a>:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">atexit</span>
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<span class="nd">@atexit</span><span class="o">.</span><span class="n">register</span>
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<span class="k">def</span> <span class="nf">goodbye</span><span class="p">():</span>
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<span class="nb">print</span><span class="p">(</span><span class="s2">"You are now leaving the Python sector."</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>This only works with functions that can be called without arguments.</p>
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<ul>
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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code> — Exit handlers</a><ul>
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<li><a class="reference internal" href="#atexit-example"><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code> Example</a></li>
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