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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>
<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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<section id="module-atexit">
<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>
<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 functions to register and unregister 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>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>When used with C-API subinterpreters, registered functions
are local to the interpreter they were registered in.</p>
</div>
<dl class="py function">
<dt class="sig sig-object py" id="atexit.register">
<span class="sig-prename descclassname"><span class="pre">atexit.</span></span><span class="sig-name descname"><span class="pre">register</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">func</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span><span class="n"><span class="pre">args</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">**</span></span><span class="n"><span class="pre">kwargs</span></span></em><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#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
saved. After all exit handlers have had a chance to run, the last exception to
be raised is re-raised.</p>
<p>This function returns <em>func</em>, which makes it possible to use it as a
decorator.</p>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="atexit.unregister">
<span class="sig-prename descclassname"><span class="pre">atexit.</span></span><span class="sig-name descname"><span class="pre">unregister</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">func</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#atexit.unregister" title="Permalink to this definition">¶</a></dt>
<dd><p>Remove <em>func</em> from the list of functions to be run at interpreter shutdown.
<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
registered. If <em>func</em> has been registered more than once, every occurrence
of that function in 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> call stack will be removed. Equality
comparisons (<code class="docutils literal notranslate"><span class="pre">==</span></code>) are used internally during unregistration, so function
references do not need to have matching identities.</p>
</dd></dl>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<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
files.</p>
</dd>
</dl>
</div>
<section id="atexit-example">
<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>
<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-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'counterfile'</span><span class="p">)</span> <span class="k">as</span> <span class="n">infile</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="n">infile</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
<span class="k">except</span> <span class="ne">FileNotFoundError</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="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'counterfile'</span><span class="p">,</span> <span class="s1">'w'</span><span class="p">)</span> <span class="k">as</span> <span class="n">outfile</span><span class="p">:</span>
<span class="n">outfile</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s1">'</span><span class="si">%d</span><span class="s1">'</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-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>
<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>
<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-python3 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="p">(</span><span class="s1">'You are now leaving the Python sector.'</span><span class="p">)</span>
</pre></div>
</div>
<p>This only works with functions that can be called without arguments.</p>
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