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<li><a class="reference internal" href="#">Policies</a><ul>
<li><a class="reference internal" href="#getting-and-setting-the-policy">Getting and Setting the Policy</a></li>
<li><a class="reference internal" href="#policy-objects">Policy Objects</a></li>
<li><a class="reference internal" href="#custom-policies">Custom Policies</a></li>
</ul>
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  <section id="policies">
<span id="asyncio-policies"></span><h1>Policies<a class="headerlink" href="#policies" title="Link to this heading">¶</a></h1>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Policies are deprecated and will be removed in Python 3.16.
Users are encouraged to use the <a class="reference internal" href="asyncio-runner.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.run()</span></code></a> function
or the <a class="reference internal" href="asyncio-runner.html#asyncio.Runner" title="asyncio.Runner"><code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.Runner</span></code></a> with <em>loop_factory</em> to use
the desired loop implementation.</p>
</div>
<p>An event loop policy is a global object
used to get and set the current <a class="reference internal" href="asyncio-eventloop.html#asyncio-event-loop"><span class="std std-ref">event loop</span></a>,
as well as create new event loops.
The default policy can be <a class="reference internal" href="#asyncio-policy-get-set"><span class="std std-ref">replaced</span></a> with
<a class="reference internal" href="#asyncio-policy-builtin"><span class="std std-ref">built-in alternatives</span></a>
to use different event loop implementations,
or substituted by a <a class="reference internal" href="#asyncio-custom-policies"><span class="std std-ref">custom policy</span></a>
that can override these behaviors.</p>
<p>The <a class="reference internal" href="#asyncio-policy-objects"><span class="std std-ref">policy object</span></a>
gets and sets a separate event loop per <em>context</em>.
This is per-thread by default,
though custom policies could define <em>context</em> differently.</p>
<p>Custom event loop policies can control the behavior of
<a class="reference internal" href="asyncio-eventloop.html#asyncio.get_event_loop" title="asyncio.get_event_loop"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_event_loop()</span></code></a>, <a class="reference internal" href="asyncio-eventloop.html#asyncio.set_event_loop" title="asyncio.set_event_loop"><code class="xref py py-func docutils literal notranslate"><span class="pre">set_event_loop()</span></code></a>, and <a class="reference internal" href="asyncio-eventloop.html#asyncio.new_event_loop" title="asyncio.new_event_loop"><code class="xref py py-func docutils literal notranslate"><span class="pre">new_event_loop()</span></code></a>.</p>
<p>Policy objects should implement the APIs defined
in the <a class="reference internal" href="#asyncio.AbstractEventLoopPolicy" title="asyncio.AbstractEventLoopPolicy"><code class="xref py py-class docutils literal notranslate"><span class="pre">AbstractEventLoopPolicy</span></code></a> abstract base class.</p>
<section id="getting-and-setting-the-policy">
<span id="asyncio-policy-get-set"></span><h2>Getting and Setting the Policy<a class="headerlink" href="#getting-and-setting-the-policy" title="Link to this heading">¶</a></h2>
<p>The following functions can be used to get and set the policy
for the current process:</p>
<dl class="py function">
<dt class="sig sig-object py" id="asyncio.get_event_loop_policy">
<span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">get_event_loop_policy</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.get_event_loop_policy" title="Link to this definition">¶</a></dt>
<dd><p>Return the current process-wide policy.</p>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.14: </span>The <code class="xref py py-func docutils literal notranslate"><span class="pre">get_event_loop_policy()</span></code> function is deprecated and
will be removed in Python 3.16.</p>
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="asyncio.set_event_loop_policy">
<span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">set_event_loop_policy</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">policy</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.set_event_loop_policy" title="Link to this definition">¶</a></dt>
<dd><p>Set the current process-wide policy to <em>policy</em>.</p>
<p>If <em>policy</em> is set to <code class="docutils literal notranslate"><span class="pre">None</span></code>, the default policy is restored.</p>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.14: </span>The <code class="xref py py-func docutils literal notranslate"><span class="pre">set_event_loop_policy()</span></code> function is deprecated and
will be removed in Python 3.16.</p>
</div>
</dd></dl>

</section>
<section id="policy-objects">
<span id="asyncio-policy-objects"></span><h2>Policy Objects<a class="headerlink" href="#policy-objects" title="Link to this heading">¶</a></h2>
<p>The abstract event loop policy base class is defined as follows:</p>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.AbstractEventLoopPolicy">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">AbstractEventLoopPolicy</span></span><a class="headerlink" href="#asyncio.AbstractEventLoopPolicy" title="Link to this definition">¶</a></dt>
<dd><p>An abstract base class for asyncio policies.</p>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.AbstractEventLoopPolicy.get_event_loop">
<span class="sig-name descname"><span class="pre">get_event_loop</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.AbstractEventLoopPolicy.get_event_loop" title="Link to this definition">¶</a></dt>
<dd><p>Get the event loop for the current context.</p>
<p>Return an event loop object implementing the
<a class="reference internal" href="asyncio-eventloop.html#asyncio.AbstractEventLoop" title="asyncio.AbstractEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">AbstractEventLoop</span></code></a> interface.</p>
<p>This method should never return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6.</span></p>
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.AbstractEventLoopPolicy.set_event_loop">
<span class="sig-name descname"><span class="pre">set_event_loop</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">loop</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.AbstractEventLoopPolicy.set_event_loop" title="Link to this definition">¶</a></dt>
<dd><p>Set the event loop for the current context to <em>loop</em>.</p>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.AbstractEventLoopPolicy.new_event_loop">
<span class="sig-name descname"><span class="pre">new_event_loop</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.AbstractEventLoopPolicy.new_event_loop" title="Link to this definition">¶</a></dt>
<dd><p>Create and return a new event loop object.</p>
<p>This method should never return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>

<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.14: </span>The <code class="xref py py-class docutils literal notranslate"><span class="pre">AbstractEventLoopPolicy</span></code> class is deprecated and
will be removed in Python 3.16.</p>
</div>
</dd></dl>

<p id="asyncio-policy-builtin">asyncio ships with the following built-in policies:</p>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.DefaultEventLoopPolicy">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">DefaultEventLoopPolicy</span></span><a class="headerlink" href="#asyncio.DefaultEventLoopPolicy" title="Link to this definition">¶</a></dt>
<dd><p>The default asyncio policy.  Uses <a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a>
on Unix and <a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> on Windows.</p>
<p>There is no need to install the default policy manually. asyncio
is configured to use the default policy automatically.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>On Windows, <a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> is now used by default.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.14: </span>The <a class="reference internal" href="asyncio-eventloop.html#asyncio.get_event_loop" title="asyncio.get_event_loop"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_event_loop()</span></code></a> method of the default asyncio policy now
raises a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a> if there is no set event loop.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.14: </span>The <code class="xref py py-class docutils literal notranslate"><span class="pre">DefaultEventLoopPolicy</span></code> class is deprecated and
will be removed in Python 3.16.</p>
</div>
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="asyncio.WindowsSelectorEventLoopPolicy">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">WindowsSelectorEventLoopPolicy</span></span><a class="headerlink" href="#asyncio.WindowsSelectorEventLoopPolicy" title="Link to this definition">¶</a></dt>
<dd><p>An alternative event loop policy that uses the
<a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a> event loop implementation.</p>
<div class="availability docutils container">
<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Windows.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.14: </span>The <code class="xref py py-class docutils literal notranslate"><span class="pre">WindowsSelectorEventLoopPolicy</span></code> class is deprecated and
will be removed in Python 3.16.</p>
</div>
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="asyncio.WindowsProactorEventLoopPolicy">
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">WindowsProactorEventLoopPolicy</span></span><a class="headerlink" href="#asyncio.WindowsProactorEventLoopPolicy" title="Link to this definition">¶</a></dt>
<dd><p>An alternative event loop policy that uses the
<a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> event loop implementation.</p>
<div class="availability docutils container">
<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Windows.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.14: </span>The <code class="xref py py-class docutils literal notranslate"><span class="pre">WindowsProactorEventLoopPolicy</span></code> class is deprecated and
will be removed in Python 3.16.</p>
</div>
</dd></dl>

</section>
<section id="custom-policies">
<span id="asyncio-custom-policies"></span><h2>Custom Policies<a class="headerlink" href="#custom-policies" title="Link to this heading">¶</a></h2>
<p>To implement a new event loop policy, it is recommended to subclass
<a class="reference internal" href="#asyncio.DefaultEventLoopPolicy" title="asyncio.DefaultEventLoopPolicy"><code class="xref py py-class docutils literal notranslate"><span class="pre">DefaultEventLoopPolicy</span></code></a> and override the methods for which
custom behavior is wanted, e.g.:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span><span class="w"> </span><span class="nc">MyEventLoopPolicy</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">DefaultEventLoopPolicy</span><span class="p">):</span>

    <span class="k">def</span><span class="w"> </span><span class="nf">get_event_loop</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="w">        </span><span class="sd">&quot;&quot;&quot;Get the event loop.</span>

<span class="sd">        This may be None or an instance of EventLoop.</span>
<span class="sd">        &quot;&quot;&quot;</span>
        <span class="n">loop</span> <span class="o">=</span> <span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="n">get_event_loop</span><span class="p">()</span>
        <span class="c1"># Do something with loop ...</span>
        <span class="k">return</span> <span class="n">loop</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">set_event_loop_policy</span><span class="p">(</span><span class="n">MyEventLoopPolicy</span><span class="p">())</span>
</pre></div>
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