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  <section id="extending">
<h1>Extending<a class="headerlink" href="#extending" title="Link to this heading">¶</a></h1>
<p>The main direction for <a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code></a> extending is writing custom <em>event loop</em>
classes. Asyncio has helpers that could be used to simplify this task.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Third-parties should reuse existing asyncio code with caution,
a new Python version is free to break backward compatibility
in <em>internal</em> part of API.</p>
</div>
<section id="writing-a-custom-event-loop">
<h2>Writing a Custom Event Loop<a class="headerlink" href="#writing-a-custom-event-loop" title="Link to this heading">¶</a></h2>
<p><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">asyncio.AbstractEventLoop</span></code></a> declares very many methods.  Implementing all them
from scratch is a tedious job.</p>
<p>A loop can get many common methods implementation for free by inheriting from
<code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.BaseEventLoop</span></code>.</p>
<p>In turn, the successor should implement a bunch of <em>private</em> methods declared but not
implemented in <code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.BaseEventLoop</span></code>.</p>
<p>For example, <code class="docutils literal notranslate"><span class="pre">loop.create_connection()</span></code> checks arguments, resolves DNS addresses, and
calls <code class="docutils literal notranslate"><span class="pre">loop._make_socket_transport()</span></code> that should be implemented by inherited class.
The <code class="docutils literal notranslate"><span class="pre">_make_socket_transport()</span></code> method is not documented and is considered as an
<em>internal</em> API.</p>
</section>
<section id="future-and-task-private-constructors">
<h2>Future and Task private constructors<a class="headerlink" href="#future-and-task-private-constructors" title="Link to this heading">¶</a></h2>
<p><a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.Future</span></code></a> and <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.Task</span></code></a> should be never created directly,
please use corresponding <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_future" title="asyncio.loop.create_future"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_future()</span></code></a> and <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_task" title="asyncio.loop.create_task"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_task()</span></code></a>,
or <a class="reference internal" href="asyncio-task.html#asyncio.create_task" title="asyncio.create_task"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.create_task()</span></code></a> factories instead.</p>
<p>However, third-party <em>event loops</em> may <em>reuse</em> built-in future and task implementations
for the sake of getting a complex and highly optimized code for free.</p>
<p>For this purpose the following, <em>private</em> constructors are listed:</p>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Future.__init__">
<span class="sig-prename descclassname"><span class="pre">Future.</span></span><span class="sig-name descname"><span class="pre">__init__</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="o"><span class="pre">*</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">loop</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Future.__init__" title="Link to this definition">¶</a></dt>
<dd><p>Create a built-in future instance.</p>
<p><em>loop</em> is an optional event loop instance.</p>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Task.__init__">
<span class="sig-prename descclassname"><span class="pre">Task.</span></span><span class="sig-name descname"><span class="pre">__init__</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">coro</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">loop</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">name</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">context</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.__init__" title="Link to this definition">¶</a></dt>
<dd><p>Create a built-in task instance.</p>
<p><em>loop</em> is an optional event loop instance. The rest of arguments are described in
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_task" title="asyncio.loop.create_task"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_task()</span></code></a> description.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.11: </span><em>context</em> argument is added.</p>
</div>
</dd></dl>

</section>
<section id="task-lifetime-support">
<h2>Task lifetime support<a class="headerlink" href="#task-lifetime-support" title="Link to this heading">¶</a></h2>
<p>A third party task implementation should call the following functions to keep a task
visible by <a class="reference internal" href="asyncio-task.html#asyncio.all_tasks" title="asyncio.all_tasks"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.all_tasks()</span></code></a> and <a class="reference internal" href="asyncio-task.html#asyncio.current_task" title="asyncio.current_task"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.current_task()</span></code></a>:</p>
<dl class="py function">
<dt class="sig sig-object py" id="asyncio._register_task">
<span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">_register_task</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">task</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio._register_task" title="Link to this definition">¶</a></dt>
<dd><p>Register a new <em>task</em> as managed by <em>asyncio</em>.</p>
<p>Call the function from a task constructor.</p>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="asyncio._unregister_task">
<span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">_unregister_task</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">task</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio._unregister_task" title="Link to this definition">¶</a></dt>
<dd><p>Unregister a <em>task</em> from <em>asyncio</em> internal structures.</p>
<p>The function should be called when a task is about to finish.</p>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="asyncio._enter_task">
<span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">_enter_task</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">loop</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">task</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio._enter_task" title="Link to this definition">¶</a></dt>
<dd><p>Switch the current task to the <em>task</em> argument.</p>
<p>Call the function just before executing a portion of embedded <em>coroutine</em>
(<a class="reference internal" href="../reference/datamodel.html#coroutine.send" title="coroutine.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">coroutine.send()</span></code></a> or <a class="reference internal" href="../reference/datamodel.html#coroutine.throw" title="coroutine.throw"><code class="xref py py-meth docutils literal notranslate"><span class="pre">coroutine.throw()</span></code></a>).</p>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="asyncio._leave_task">
<span class="sig-prename descclassname"><span class="pre">asyncio.</span></span><span class="sig-name descname"><span class="pre">_leave_task</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">loop</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">task</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio._leave_task" title="Link to this definition">¶</a></dt>
<dd><p>Switch the current task back from <em>task</em> to <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<p>Call the function just after <a class="reference internal" href="../reference/datamodel.html#coroutine.send" title="coroutine.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">coroutine.send()</span></code></a> or <a class="reference internal" href="../reference/datamodel.html#coroutine.throw" title="coroutine.throw"><code class="xref py py-meth docutils literal notranslate"><span class="pre">coroutine.throw()</span></code></a>
execution.</p>
</dd></dl>

</section>
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<li><a class="reference internal" href="#future-and-task-private-constructors">Future and Task private constructors</a></li>
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