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Code Editor : asyncio-eventloop.html

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 <h3><a href="../contents.html">Table of Contents</a></h3>
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<li><a class="reference internal" href="#">Event Loop</a><ul>
<li><a class="reference internal" href="#event-loop-methods">Event Loop Methods</a><ul>
<li><a class="reference internal" href="#running-and-stopping-the-loop">Running and stopping the loop</a></li>
<li><a class="reference internal" href="#scheduling-callbacks">Scheduling callbacks</a></li>
<li><a class="reference internal" href="#scheduling-delayed-callbacks">Scheduling delayed callbacks</a></li>
<li><a class="reference internal" href="#creating-futures-and-tasks">Creating Futures and Tasks</a></li>
<li><a class="reference internal" href="#opening-network-connections">Opening network connections</a></li>
<li><a class="reference internal" href="#creating-network-servers">Creating network servers</a></li>
<li><a class="reference internal" href="#transferring-files">Transferring files</a></li>
<li><a class="reference internal" href="#tls-upgrade">TLS Upgrade</a></li>
<li><a class="reference internal" href="#watching-file-descriptors">Watching file descriptors</a></li>
<li><a class="reference internal" href="#working-with-socket-objects-directly">Working with socket objects directly</a></li>
<li><a class="reference internal" href="#dns">DNS</a></li>
<li><a class="reference internal" href="#working-with-pipes">Working with pipes</a></li>
<li><a class="reference internal" href="#unix-signals">Unix signals</a></li>
<li><a class="reference internal" href="#executing-code-in-thread-or-process-pools">Executing code in thread or process pools</a></li>
<li><a class="reference internal" href="#error-handling-api">Error Handling API</a></li>
<li><a class="reference internal" href="#enabling-debug-mode">Enabling debug mode</a></li>
<li><a class="reference internal" href="#running-subprocesses">Running Subprocesses</a></li>
</ul>
</li>
<li><a class="reference internal" href="#callback-handles">Callback Handles</a></li>
<li><a class="reference internal" href="#server-objects">Server Objects</a></li>
<li><a class="reference internal" href="#event-loop-implementations">Event Loop Implementations</a></li>
<li><a class="reference internal" href="#examples">Examples</a><ul>
<li><a class="reference internal" href="#hello-world-with-call-soon">Hello World with call_soon()</a></li>
<li><a class="reference internal" href="#display-the-current-date-with-call-later">Display the current date with call_later()</a></li>
<li><a class="reference internal" href="#watch-a-file-descriptor-for-read-events">Watch a file descriptor for read events</a></li>
<li><a class="reference internal" href="#set-signal-handlers-for-sigint-and-sigterm">Set signal handlers for SIGINT and SIGTERM</a></li>
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 <section id="event-loop">
<h1>Event Loop<a class="headerlink" href="#event-loop" title="Permalink to this headline">¶</a></h1>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.10/Lib/asyncio/events.py">Lib/asyncio/events.py</a>,
<a class="reference external" href="https://github.com/python/cpython/tree/3.10/Lib/asyncio/base_events.py">Lib/asyncio/base_events.py</a>
<hr class="docutils" />
Preface
The event loop is the core of every asyncio application.
Event loops run asynchronous tasks and callbacks, perform network
IO operations, and run subprocesses.
Application developers should typically use the high-level asyncio functions,
such as <a class="reference internal" href="asyncio-task.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate">asyncio.run()</code></a>, and should rarely need to reference the loop
object or call its methods. This section is intended mostly for authors
of lower-level code, libraries, and frameworks, who need finer control over
the event loop behavior.
Obtaining the Event Loop
The following low-level functions can be used to get, set, or create
an event loop:
<dl class="py function">
<dt class="sig sig-object py" id="asyncio.get_running_loop">
asyncio.get_running_loop()<a class="headerlink" href="#asyncio.get_running_loop" title="Permalink to this definition">¶</a></dt>
<dd>Return the running event loop in the current OS thread.
Raise a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> if there is no running event loop.
This function can only be called from a coroutine or a callback.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="asyncio.get_event_loop">
asyncio.get_event_loop()<a class="headerlink" href="#asyncio.get_event_loop" title="Permalink to this definition">¶</a></dt>
<dd>Get the current event loop.
When called from a coroutine or a callback (e.g. scheduled with
call_soon or similar API), this function will always return the
running event loop.
If there is no running event loop set, the function will return
the result of the <code class="docutils literal notranslate">get_event_loop_policy().get_event_loop()</code> call.
Because this function has rather complex behavior (especially
when custom event loop policies are in use), using the
<a class="reference internal" href="#asyncio.get_running_loop" title="asyncio.get_running_loop"><code class="xref py py-func docutils literal notranslate">get_running_loop()</code></a> function is preferred to <a class="reference internal" href="#asyncio.get_event_loop" title="asyncio.get_event_loop"><code class="xref py py-func docutils literal notranslate">get_event_loop()</code></a>
in coroutines and callbacks.
As noted above, consider using the higher-level <a class="reference internal" href="asyncio-task.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate">asyncio.run()</code></a> function,
instead of using these lower level functions to manually create and close an
event loop.
<div class="admonition note">
Note
In Python versions 3.10.0–3.10.8 and 3.11.0 this function
(and other functions which use it implicitly) emitted a
<a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> if there was no running event loop, even if
the current loop was set on the policy.
In Python versions 3.10.9, 3.11.1 and 3.12 they emit a
<a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> if there is no running event loop and no
current loop is set.
In some future Python release this will become an error.
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="asyncio.set_event_loop">
asyncio.set_event_loop(loop)<a class="headerlink" href="#asyncio.set_event_loop" title="Permalink to this definition">¶</a></dt>
<dd>Set loop as the current event loop for the current OS thread.
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="asyncio.new_event_loop">
asyncio.new_event_loop()<a class="headerlink" href="#asyncio.new_event_loop" title="Permalink to this definition">¶</a></dt>
<dd>Create and return a new event loop object.
</dd></dl>

Note that the behaviour of <a class="reference internal" href="#asyncio.get_event_loop" title="asyncio.get_event_loop"><code class="xref py py-func docutils literal notranslate">get_event_loop()</code></a>, <a class="reference internal" href="#asyncio.set_event_loop" title="asyncio.set_event_loop"><code class="xref py py-func docutils literal notranslate">set_event_loop()</code></a>,
and <a class="reference internal" href="#asyncio.new_event_loop" title="asyncio.new_event_loop"><code class="xref py py-func docutils literal notranslate">new_event_loop()</code></a> functions can be altered by
<a class="reference internal" href="asyncio-policy.html#asyncio-policies">setting a custom event loop policy</a>.
Contents
This documentation page contains the following sections:
<ul class="simple">
<li>The <a class="reference internal" href="#event-loop-methods">Event Loop Methods</a> section is the reference documentation of
the event loop APIs;</li>
<li>The <a class="reference internal" href="#callback-handles">Callback Handles</a> section documents the <a class="reference internal" href="#asyncio.Handle" title="asyncio.Handle"><code class="xref py py-class docutils literal notranslate">Handle</code></a> and
<a class="reference internal" href="#asyncio.TimerHandle" title="asyncio.TimerHandle"><code class="xref py py-class docutils literal notranslate">TimerHandle</code></a> instances which are returned from scheduling
methods such as <a class="reference internal" href="#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate">loop.call_soon()</code></a> and <a class="reference internal" href="#asyncio.loop.call_later" title="asyncio.loop.call_later"><code class="xref py py-meth docutils literal notranslate">loop.call_later()</code></a>;</li>
<li>The <a class="reference internal" href="#server-objects">Server Objects</a> section documents types returned from
event loop methods like <a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">loop.create_server()</code></a>;</li>
<li>The <a class="reference internal" href="#event-loop-implementations">Event Loop Implementations</a> section documents the
<a class="reference internal" href="#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate">SelectorEventLoop</code></a> and <a class="reference internal" href="#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate">ProactorEventLoop</code></a> classes;</li>
<li>The <a class="reference internal" href="#examples">Examples</a> section showcases how to work with some event
loop APIs.</li>
</ul>
<section id="event-loop-methods">
<h2>Event Loop Methods<a class="headerlink" href="#event-loop-methods" title="Permalink to this headline">¶</a></h2>
Event loops have low-level APIs for the following:
<div class="contents local topic" id="contents">
<ul class="simple">
<li><a class="reference internal" href="#running-and-stopping-the-loop" id="id1">Running and stopping the loop</a></li>
<li><a class="reference internal" href="#scheduling-callbacks" id="id2">Scheduling callbacks</a></li>
<li><a class="reference internal" href="#scheduling-delayed-callbacks" id="id3">Scheduling delayed callbacks</a></li>
<li><a class="reference internal" href="#creating-futures-and-tasks" id="id4">Creating Futures and Tasks</a></li>
<li><a class="reference internal" href="#opening-network-connections" id="id5">Opening network connections</a></li>
<li><a class="reference internal" href="#creating-network-servers" id="id6">Creating network servers</a></li>
<li><a class="reference internal" href="#transferring-files" id="id7">Transferring files</a></li>
<li><a class="reference internal" href="#tls-upgrade" id="id8">TLS Upgrade</a></li>
<li><a class="reference internal" href="#watching-file-descriptors" id="id9">Watching file descriptors</a></li>
<li><a class="reference internal" href="#working-with-socket-objects-directly" id="id10">Working with socket objects directly</a></li>
<li><a class="reference internal" href="#dns" id="id11">DNS</a></li>
<li><a class="reference internal" href="#working-with-pipes" id="id12">Working with pipes</a></li>
<li><a class="reference internal" href="#unix-signals" id="id13">Unix signals</a></li>
<li><a class="reference internal" href="#executing-code-in-thread-or-process-pools" id="id14">Executing code in thread or process pools</a></li>
<li><a class="reference internal" href="#error-handling-api" id="id15">Error Handling API</a></li>
<li><a class="reference internal" href="#enabling-debug-mode" id="id16">Enabling debug mode</a></li>
<li><a class="reference internal" href="#running-subprocesses" id="id17">Running Subprocesses</a></li>
</ul>
</div>
<section id="running-and-stopping-the-loop">
<h3><a class="toc-backref" href="#id1">Running and stopping the loop</a><a class="headerlink" href="#running-and-stopping-the-loop" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.run_until_complete">
loop.run_until_complete(future)<a class="headerlink" href="#asyncio.loop.run_until_complete" title="Permalink to this definition">¶</a></dt>
<dd>Run until the future (an instance of <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">Future</code></a>) has
completed.
If the argument is a <a class="reference internal" href="asyncio-task.html#coroutine">coroutine object</a> it
is implicitly scheduled to run as a <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate">asyncio.Task</code></a>.
Return the Future’s result or raise its exception.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.run_forever">
loop.run_forever()<a class="headerlink" href="#asyncio.loop.run_forever" title="Permalink to this definition">¶</a></dt>
<dd>Run the event loop until <a class="reference internal" href="#asyncio.loop.stop" title="asyncio.loop.stop"><code class="xref py py-meth docutils literal notranslate">stop()</code></a> is called.
If <a class="reference internal" href="#asyncio.loop.stop" title="asyncio.loop.stop"><code class="xref py py-meth docutils literal notranslate">stop()</code></a> is called before <a class="reference internal" href="#asyncio.loop.run_forever" title="asyncio.loop.run_forever"><code class="xref py py-meth docutils literal notranslate">run_forever()</code></a> is called,
the loop will poll the I/O selector once with a timeout of zero,
run all callbacks scheduled in response to I/O events (and
those that were already scheduled), and then exit.
If <a class="reference internal" href="#asyncio.loop.stop" title="asyncio.loop.stop"><code class="xref py py-meth docutils literal notranslate">stop()</code></a> is called while <a class="reference internal" href="#asyncio.loop.run_forever" title="asyncio.loop.run_forever"><code class="xref py py-meth docutils literal notranslate">run_forever()</code></a> is running,
the loop will run the current batch of callbacks and then exit.
Note that new callbacks scheduled by callbacks will not run in this
case; instead, they will run the next time <a class="reference internal" href="#asyncio.loop.run_forever" title="asyncio.loop.run_forever"><code class="xref py py-meth docutils literal notranslate">run_forever()</code></a> or
<a class="reference internal" href="#asyncio.loop.run_until_complete" title="asyncio.loop.run_until_complete"><code class="xref py py-meth docutils literal notranslate">run_until_complete()</code></a> is called.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.stop">
loop.stop()<a class="headerlink" href="#asyncio.loop.stop" title="Permalink to this definition">¶</a></dt>
<dd>Stop the event loop.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.is_running">
loop.is_running()<a class="headerlink" href="#asyncio.loop.is_running" title="Permalink to this definition">¶</a></dt>
<dd>Return <code class="docutils literal notranslate">True</code> if the event loop is currently running.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.is_closed">
loop.is_closed()<a class="headerlink" href="#asyncio.loop.is_closed" title="Permalink to this definition">¶</a></dt>
<dd>Return <code class="docutils literal notranslate">True</code> if the event loop was closed.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.close">
loop.close()<a class="headerlink" href="#asyncio.loop.close" title="Permalink to this definition">¶</a></dt>
<dd>Close the event loop.
The loop must not be running when this function is called.
Any pending callbacks will be discarded.
This method clears all queues and shuts down the executor, but does
not wait for the executor to finish.
This method is idempotent and irreversible. No other methods
should be called after the event loop is closed.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.shutdown_asyncgens">
coroutine loop.shutdown_asyncgens()<a class="headerlink" href="#asyncio.loop.shutdown_asyncgens" title="Permalink to this definition">¶</a></dt>
<dd>Schedule all currently open <a class="reference internal" href="../glossary.html#term-asynchronous-generator">asynchronous generator</a> objects to
close with an <a class="reference internal" href="../reference/expressions.html#agen.aclose" title="agen.aclose"><code class="xref py py-meth docutils literal notranslate">aclose()</code></a> call. After calling this method,
the event loop will issue a warning if a new asynchronous generator
is iterated. This should be used to reliably finalize all scheduled
asynchronous generators.
Note that there is no need to call this function when
<a class="reference internal" href="asyncio-task.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate">asyncio.run()</code></a> is used.
Example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>try:
 loop.run_forever()
finally:
 loop.run_until_complete(loop.shutdown_asyncgens())
 loop.close()
</pre></div>
</div>
<div class="versionadded">
New in version 3.6.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.shutdown_default_executor">
coroutine loop.shutdown_default_executor()<a class="headerlink" href="#asyncio.loop.shutdown_default_executor" title="Permalink to this definition">¶</a></dt>
<dd>Schedule the closure of the default executor and wait for it to join all of
the threads in the <a class="reference internal" href="concurrent.futures.html#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate">ThreadPoolExecutor</code></a>.
Once this method has been called,
using the default executor with <a class="reference internal" href="#asyncio.loop.run_in_executor" title="asyncio.loop.run_in_executor"><code class="xref py py-meth docutils literal notranslate">loop.run_in_executor()</code></a>
will raise a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a>.
<div class="admonition note">
Note
Do not call this method when using <a class="reference internal" href="asyncio-task.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate">asyncio.run()</code></a>,
as the latter handles default executor shutdown automatically.
</div>
<div class="versionadded">
New in version 3.9.
</div>
</dd></dl>

</section>
<section id="scheduling-callbacks">
<h3><a class="toc-backref" href="#id2">Scheduling callbacks</a><a class="headerlink" href="#scheduling-callbacks" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.call_soon">
loop.call_soon(callback, *args, context=None)<a class="headerlink" href="#asyncio.loop.call_soon" title="Permalink to this definition">¶</a></dt>
<dd>Schedule the callback <a class="reference internal" href="../glossary.html#term-callback">callback</a> to be called with
args arguments at the next iteration of the event loop.
Return an instance of <a class="reference internal" href="#asyncio.Handle" title="asyncio.Handle"><code class="xref py py-class docutils literal notranslate">asyncio.Handle</code></a>,
which can be used later to cancel the callback.
Callbacks are called in the order in which they are registered.
Each callback will be called exactly once.
The optional keyword-only context argument specifies a
custom <a class="reference internal" href="contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate">contextvars.Context</code></a> for the callback to run in.
Callbacks use the current context when no context is provided.
Unlike <a class="reference internal" href="#asyncio.loop.call_soon_threadsafe" title="asyncio.loop.call_soon_threadsafe"><code class="xref py py-meth docutils literal notranslate">call_soon_threadsafe()</code></a>, this method is not thread-safe.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.call_soon_threadsafe">
loop.call_soon_threadsafe(callback, *args, context=None)<a class="headerlink" href="#asyncio.loop.call_soon_threadsafe" title="Permalink to this definition">¶</a></dt>
<dd>A thread-safe variant of <a class="reference internal" href="#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate">call_soon()</code></a>. When scheduling callbacks from
another thread, this function must be used, since <a class="reference internal" href="#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate">call_soon()</code></a> is not
thread-safe.
Raises <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> if called on a loop that’s been closed.
This can happen on a secondary thread when the main application is
shutting down.
See the <a class="reference internal" href="asyncio-dev.html#asyncio-multithreading">concurrency and multithreading</a>
section of the documentation.
</dd></dl>

<div class="versionchanged">
Changed in version 3.7: The context keyword-only parameter was added. See <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0567">PEP 567</a>
for more details.
</div>
<div class="admonition note" id="asyncio-pass-keywords">
Note
Most <a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate">asyncio</code></a> scheduling functions don’t allow passing
keyword arguments. To do that, use <a class="reference internal" href="functools.html#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate">functools.partial()</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre># will schedule &quot;print(&quot;Hello&quot;, flush=True)&quot;
loop.call_soon(
 functools.partial(print, &quot;Hello&quot;, flush=True))
</pre></div>
</div>
Using partial objects is usually more convenient than using lambdas,
as asyncio can render partial objects better in debug and error
messages.
</div>
</section>
<section id="scheduling-delayed-callbacks">
<h3><a class="toc-backref" href="#id3">Scheduling delayed callbacks</a><a class="headerlink" href="#scheduling-delayed-callbacks" title="Permalink to this headline">¶</a></h3>
Event loop provides mechanisms to schedule callback functions
to be called at some point in the future. Event loop uses monotonic
clocks to track time.
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.call_later">
loop.call_later(delay, callback, *args, context=None)<a class="headerlink" href="#asyncio.loop.call_later" title="Permalink to this definition">¶</a></dt>
<dd>Schedule callback to be called after the given delay
number of seconds (can be either an int or a float).
An instance of <a class="reference internal" href="#asyncio.TimerHandle" title="asyncio.TimerHandle"><code class="xref py py-class docutils literal notranslate">asyncio.TimerHandle</code></a> is returned which can
be used to cancel the callback.
callback will be called exactly once. If two callbacks are
scheduled for exactly the same time, the order in which they
are called is undefined.
The optional positional args will be passed to the callback when
it is called. If you want the callback to be called with keyword
arguments use <a class="reference internal" href="functools.html#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate">functools.partial()</code></a>.
An optional keyword-only context argument allows specifying a
custom <a class="reference internal" href="contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate">contextvars.Context</code></a> for the callback to run in.
The current context is used when no context is provided.
<div class="versionchanged">
Changed in version 3.7: The context keyword-only parameter was added. See <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0567">PEP 567</a>
for more details.
</div>
<div class="versionchanged">
Changed in version 3.8: In Python 3.7 and earlier with the default event loop implementation,
the delay could not exceed one day.
This has been fixed in Python 3.8.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.call_at">
loop.call_at(when, callback, *args, context=None)<a class="headerlink" href="#asyncio.loop.call_at" title="Permalink to this definition">¶</a></dt>
<dd>Schedule callback to be called at the given absolute timestamp
when (an int or a float), using the same time reference as
<a class="reference internal" href="#asyncio.loop.time" title="asyncio.loop.time"><code class="xref py py-meth docutils literal notranslate">loop.time()</code></a>.
This method’s behavior is the same as <a class="reference internal" href="#asyncio.loop.call_later" title="asyncio.loop.call_later"><code class="xref py py-meth docutils literal notranslate">call_later()</code></a>.
An instance of <a class="reference internal" href="#asyncio.TimerHandle" title="asyncio.TimerHandle"><code class="xref py py-class docutils literal notranslate">asyncio.TimerHandle</code></a> is returned which can
be used to cancel the callback.
<div class="versionchanged">
Changed in version 3.7: The context keyword-only parameter was added. See <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0567">PEP 567</a>
for more details.
</div>
<div class="versionchanged">
Changed in version 3.8: In Python 3.7 and earlier with the default event loop implementation,
the difference between when and the current time could not exceed
one day. This has been fixed in Python 3.8.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.time">
loop.time()<a class="headerlink" href="#asyncio.loop.time" title="Permalink to this definition">¶</a></dt>
<dd>Return the current time, as a <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a> value, according to
the event loop’s internal monotonic clock.
</dd></dl>

<div class="admonition note">
Note
<div class="versionchanged">
Changed in version 3.8: In Python 3.7 and earlier timeouts (relative delay or absolute when)
should not exceed one day. This has been fixed in Python 3.8.
</div>
</div>
<div class="admonition seealso">
See also
The <a class="reference internal" href="asyncio-task.html#asyncio.sleep" title="asyncio.sleep"><code class="xref py py-func docutils literal notranslate">asyncio.sleep()</code></a> function.
</div>
</section>
<section id="creating-futures-and-tasks">
<h3><a class="toc-backref" href="#id4">Creating Futures and Tasks</a><a class="headerlink" href="#creating-futures-and-tasks" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.create_future">
loop.create_future()<a class="headerlink" href="#asyncio.loop.create_future" title="Permalink to this definition">¶</a></dt>
<dd>Create an <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">asyncio.Future</code></a> object attached to the event loop.
This is the preferred way to create Futures in asyncio. This lets
third-party event loops provide alternative implementations of
the Future object (with better performance or instrumentation).
<div class="versionadded">
New in version 3.5.2.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.create_task">
loop.create_task(coro, *, name=None)<a class="headerlink" href="#asyncio.loop.create_task" title="Permalink to this definition">¶</a></dt>
<dd>Schedule the execution of <a class="reference internal" href="asyncio-task.html#coroutine">coroutine</a> coro.
Return a <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate">Task</code></a> object.
Third-party event loops can use their own subclass of <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate">Task</code></a>
for interoperability. In this case, the result type is a subclass
of <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate">Task</code></a>.
If the name argument is provided and not <code class="docutils literal notranslate">None</code>, it is set as
the name of the task using <a class="reference internal" href="asyncio-task.html#asyncio.Task.set_name" title="asyncio.Task.set_name"><code class="xref py py-meth docutils literal notranslate">Task.set_name()</code></a>.
<div class="versionchanged">
Changed in version 3.8: Added the name parameter.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.set_task_factory">
loop.set_task_factory(factory)<a class="headerlink" href="#asyncio.loop.set_task_factory" title="Permalink to this definition">¶</a></dt>
<dd>Set a task factory that will be used by
<a class="reference internal" href="#asyncio.loop.create_task" title="asyncio.loop.create_task"><code class="xref py py-meth docutils literal notranslate">loop.create_task()</code></a>.
If factory is <code class="docutils literal notranslate">None</code> the default task factory will be set.
Otherwise, factory must be a callable with the signature matching
<code class="docutils literal notranslate">(loop, coro)</code>, where loop is a reference to the active
event loop, and coro is a coroutine object. The callable
must return a <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">asyncio.Future</code></a>-compatible object.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.get_task_factory">
loop.get_task_factory()<a class="headerlink" href="#asyncio.loop.get_task_factory" title="Permalink to this definition">¶</a></dt>
<dd>Return a task factory or <code class="docutils literal notranslate">None</code> if the default one is in use.
</dd></dl>

</section>
<section id="opening-network-connections">
<h3><a class="toc-backref" href="#id5">Opening network connections</a><a class="headerlink" href="#opening-network-connections" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.create_connection">
coroutine loop.create_connection(protocol_factory, host=None, port=None, *, ssl=None, family=0, proto=0, flags=0, sock=None, local_addr=None, server_hostname=None, ssl_handshake_timeout=None, happy_eyeballs_delay=None, interleave=None)<a class="headerlink" href="#asyncio.loop.create_connection" title="Permalink to this definition">¶</a></dt>
<dd>Open a streaming transport connection to a given
address specified by host and port.
The socket family can be either <a class="reference internal" href="socket.html#socket.AF_INET" title="socket.AF_INET"><code class="xref py py-data docutils literal notranslate">AF_INET</code></a> or
<a class="reference internal" href="socket.html#socket.AF_INET6" title="socket.AF_INET6"><code class="xref py py-data docutils literal notranslate">AF_INET6</code></a> depending on host (or the family
argument, if provided).
The socket type will be <a class="reference internal" href="socket.html#socket.SOCK_STREAM" title="socket.SOCK_STREAM"><code class="xref py py-data docutils literal notranslate">SOCK_STREAM</code></a>.
protocol_factory must be a callable returning an
<a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">asyncio protocol</a> implementation.
This method will try to establish the connection in the background.
When successful, it returns a <code class="docutils literal notranslate">(transport, protocol)</code> pair.
The chronological synopsis of the underlying operation is as follows:
<ol class="arabic simple">
<li>The connection is established and a <a class="reference internal" href="asyncio-protocol.html#asyncio-transport">transport</a>
is created for it.</li>
<li>protocol_factory is called without arguments and is expected to
return a <a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">protocol</a> instance.</li>
<li>The protocol instance is coupled with the transport by calling its
<a class="reference internal" href="asyncio-protocol.html#asyncio.BaseProtocol.connection_made" title="asyncio.BaseProtocol.connection_made"><code class="xref py py-meth docutils literal notranslate">connection_made()</code></a> method.</li>
<li>A <code class="docutils literal notranslate">(transport, protocol)</code> tuple is returned on success.</li>
</ol>
The created transport is an implementation-dependent bidirectional
stream.
Other arguments:
<ul>
<li>ssl: if given and not false, a SSL/TLS transport is created
(by default a plain TCP transport is created). If ssl is
a <a class="reference internal" href="ssl.html#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate">ssl.SSLContext</code></a> object, this context is used to create
the transport; if ssl is <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a>, a default context returned
from <a class="reference internal" href="ssl.html#ssl.create_default_context" title="ssl.create_default_context"><code class="xref py py-func docutils literal notranslate">ssl.create_default_context()</code></a> is used.
<div class="admonition seealso">
See also
<a class="reference internal" href="ssl.html#ssl-security">SSL/TLS security considerations</a>
</div>
</li>
<li>server_hostname sets or overrides the hostname that the target
server’s certificate will be matched against. Should only be passed
if ssl is not <code class="docutils literal notranslate">None</code>. By default the value of the host argument
is used. If host is empty, there is no default and you must pass a
value for server_hostname. If server_hostname is an empty
string, hostname matching is disabled (which is a serious security
risk, allowing for potential man-in-the-middle attacks).</li>
<li>family, proto, flags are the optional address family, protocol
and flags to be passed through to getaddrinfo() for host resolution.
If given, these should all be integers from the corresponding
<a class="reference internal" href="socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate">socket</code></a> module constants.</li>
<li>happy_eyeballs_delay, if given, enables Happy Eyeballs for this
connection. It should
be a floating-point number representing the amount of time in seconds
to wait for a connection attempt to complete, before starting the next
attempt in parallel. This is the “Connection Attempt Delay” as defined
in <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc8305.html">RFC 8305</a>. A sensible default value recommended by the RFC is <code class="docutils literal notranslate">0.25</code>
(250 milliseconds).</li>
<li>interleave controls address reordering when a host name resolves to
multiple IP addresses.
If <code class="docutils literal notranslate">0</code> or unspecified, no reordering is done, and addresses are
tried in the order returned by <a class="reference internal" href="#asyncio.loop.getaddrinfo" title="asyncio.loop.getaddrinfo"><code class="xref py py-meth docutils literal notranslate">getaddrinfo()</code></a>. If a positive integer
is specified, the addresses are interleaved by address family, and the
given integer is interpreted as “First Address Family Count” as defined
in <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc8305.html">RFC 8305</a>. The default is <code class="docutils literal notranslate">0</code> if happy_eyeballs_delay is not
specified, and <code class="docutils literal notranslate">1</code> if it is.</li>
<li>sock, if given, should be an existing, already connected
<a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate">socket.socket</code></a> object to be used by the transport.
If sock is given, none of host, port, family, proto, flags,
happy_eyeballs_delay, interleave
and local_addr should be specified.
<div class="admonition note">
Note
The sock argument transfers ownership of the socket to the
transport created. To close the socket, call the transport’s
<a class="reference internal" href="asyncio-protocol.html#asyncio.BaseTransport.close" title="asyncio.BaseTransport.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a> method.
</div>
</li>
<li>local_addr, if given, is a <code class="docutils literal notranslate">(local_host, local_port)</code> tuple used
to bind the socket locally. The local_host and local_port
are looked up using <code class="docutils literal notranslate">getaddrinfo()</code>, similarly to host and port.</li>
<li>ssl_handshake_timeout is (for a TLS connection) the time in seconds
to wait for the TLS handshake to complete before aborting the connection.
<code class="docutils literal notranslate">60.0</code> seconds if <code class="docutils literal notranslate">None</code> (default).</li>
</ul>
<div class="versionchanged">
Changed in version 3.5: Added support for SSL/TLS in <a class="reference internal" href="#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate">ProactorEventLoop</code></a>.
</div>
<div class="versionchanged">
Changed in version 3.6: The socket option <code class="xref py py-data docutils literal notranslate">TCP_NODELAY</code> is set by default
for all TCP connections.
</div>
<div class="versionchanged">
Changed in version 3.7: Added the ssl_handshake_timeout parameter.
</div>
<div class="versionchanged">
Changed in version 3.8: Added the happy_eyeballs_delay and interleave parameters.
Happy Eyeballs Algorithm: Success with Dual-Stack Hosts.
When a server’s IPv4 path and protocol are working, but the server’s
IPv6 path and protocol are not working, a dual-stack client
application experiences significant connection delay compared to an
IPv4-only client. This is undesirable because it causes the
dual-stack client to have a worse user experience. This document
specifies requirements for algorithms that reduce this user-visible
delay and provides an algorithm.
For more information: <a class="reference external" href="https://tools.ietf.org/html/rfc6555">https://tools.ietf.org/html/rfc6555</a>
</div>
<div class="admonition seealso">
See also
The <a class="reference internal" href="asyncio-stream.html#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate">open_connection()</code></a> function is a high-level alternative
API. It returns a pair of (<a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate">StreamReader</code></a>, <a class="reference internal" href="asyncio-stream.html#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate">StreamWriter</code></a>)
that can be used directly in async/await code.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.create_datagram_endpoint">
coroutine loop.create_datagram_endpoint(protocol_factory, local_addr=None, remote_addr=None, *, family=0, proto=0, flags=0, reuse_address=None, reuse_port=None, allow_broadcast=None, sock=None)<a class="headerlink" href="#asyncio.loop.create_datagram_endpoint" title="Permalink to this definition">¶</a></dt>
<dd><div class="admonition note">
Note
The parameter reuse_address is no longer supported, as using
<code class="xref py py-data docutils literal notranslate">SO_REUSEADDR</code> poses a significant security concern for
UDP. Explicitly passing <code class="docutils literal notranslate">reuse_address=True</code> will raise an exception.
When multiple processes with differing UIDs assign sockets to an
identical UDP socket address with <code class="docutils literal notranslate">SO_REUSEADDR</code>, incoming packets can
become randomly distributed among the sockets.
For supported platforms, reuse_port can be used as a replacement for
similar functionality. With reuse_port,
<code class="xref py py-data docutils literal notranslate">SO_REUSEPORT</code> is used instead, which specifically
prevents processes with differing UIDs from assigning sockets to the same
socket address.
</div>
Create a datagram connection.
The socket family can be either <a class="reference internal" href="socket.html#socket.AF_INET" title="socket.AF_INET"><code class="xref py py-data docutils literal notranslate">AF_INET</code></a>,
<a class="reference internal" href="socket.html#socket.AF_INET6" title="socket.AF_INET6"><code class="xref py py-data docutils literal notranslate">AF_INET6</code></a>, or <a class="reference internal" href="socket.html#socket.AF_UNIX" title="socket.AF_UNIX"><code class="xref py py-data docutils literal notranslate">AF_UNIX</code></a>,
depending on host (or the family argument, if provided).
The socket type will be <a class="reference internal" href="socket.html#socket.SOCK_DGRAM" title="socket.SOCK_DGRAM"><code class="xref py py-data docutils literal notranslate">SOCK_DGRAM</code></a>.
protocol_factory must be a callable returning a
<a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">protocol</a> implementation.
A tuple of <code class="docutils literal notranslate">(transport, protocol)</code> is returned on success.
Other arguments:
<ul>
<li>local_addr, if given, is a <code class="docutils literal notranslate">(local_host, local_port)</code> tuple used
to bind the socket locally. The local_host and local_port
are looked up using <a class="reference internal" href="#asyncio.loop.getaddrinfo" title="asyncio.loop.getaddrinfo"><code class="xref py py-meth docutils literal notranslate">getaddrinfo()</code></a>.</li>
<li>remote_addr, if given, is a <code class="docutils literal notranslate">(remote_host, remote_port)</code> tuple used
to connect the socket to a remote address. The remote_host and
remote_port are looked up using <a class="reference internal" href="#asyncio.loop.getaddrinfo" title="asyncio.loop.getaddrinfo"><code class="xref py py-meth docutils literal notranslate">getaddrinfo()</code></a>.</li>
<li>family, proto, flags are the optional address family, protocol
and flags to be passed through to <a class="reference internal" href="#asyncio.loop.getaddrinfo" title="asyncio.loop.getaddrinfo"><code class="xref py py-meth docutils literal notranslate">getaddrinfo()</code></a> for host
resolution. If given, these should all be integers from the
corresponding <a class="reference internal" href="socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate">socket</code></a> module constants.</li>
<li>reuse_port tells the kernel to allow this endpoint to be bound to the
same port as other existing endpoints are bound to, so long as they all
set this flag when being created. This option is not supported on Windows
and some Unixes. If the <code class="xref py py-data docutils literal notranslate">SO_REUSEPORT</code> constant is not
defined then this capability is unsupported.</li>
<li>allow_broadcast tells the kernel to allow this endpoint to send
messages to the broadcast address.</li>
<li>sock can optionally be specified in order to use a preexisting,
already connected, <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate">socket.socket</code></a> object to be used by the
transport. If specified, local_addr and remote_addr should be omitted
(must be <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate">None</code></a>).
<div class="admonition note">
Note
The sock argument transfers ownership of the socket to the
transport created. To close the socket, call the transport’s
<a class="reference internal" href="asyncio-protocol.html#asyncio.BaseTransport.close" title="asyncio.BaseTransport.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a> method.
</div>
</li>
</ul>
See <a class="reference internal" href="asyncio-protocol.html#asyncio-udp-echo-client-protocol">UDP echo client protocol</a> and
<a class="reference internal" href="asyncio-protocol.html#asyncio-udp-echo-server-protocol">UDP echo server protocol</a> examples.
<div class="versionchanged">
Changed in version 3.4.4: The family, proto, flags, reuse_address, reuse_port,
*allow_broadcast, and sock parameters were added.
</div>
<div class="versionchanged">
Changed in version 3.8.1: The reuse_address parameter is no longer supported due to security
concerns.
</div>
<div class="versionchanged">
Changed in version 3.8: Added support for Windows.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.create_unix_connection">
coroutine loop.create_unix_connection(protocol_factory, path=None, *, ssl=None, sock=None, server_hostname=None, ssl_handshake_timeout=None)<a class="headerlink" href="#asyncio.loop.create_unix_connection" title="Permalink to this definition">¶</a></dt>
<dd>Create a Unix connection.
The socket family will be <a class="reference internal" href="socket.html#socket.AF_UNIX" title="socket.AF_UNIX"><code class="xref py py-data docutils literal notranslate">AF_UNIX</code></a>; socket
type will be <a class="reference internal" href="socket.html#socket.SOCK_STREAM" title="socket.SOCK_STREAM"><code class="xref py py-data docutils literal notranslate">SOCK_STREAM</code></a>.
A tuple of <code class="docutils literal notranslate">(transport, protocol)</code> is returned on success.
path is the name of a Unix domain socket and is required,
unless a sock parameter is specified. Abstract Unix sockets,
<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>, <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a>, and <a class="reference internal" href="pathlib.html#pathlib.Path" title="pathlib.Path"><code class="xref py py-class docutils literal notranslate">Path</code></a> paths are
supported.
See the documentation of the <a class="reference internal" href="#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate">loop.create_connection()</code></a> method
for information about arguments to this method.
<a class="reference internal" href="intro.html#availability">Availability</a>: Unix.
<div class="versionchanged">
Changed in version 3.7: Added the ssl_handshake_timeout parameter.
The path parameter can now be a <a class="reference internal" href="../glossary.html#term-path-like-object">path-like object</a>.
</div>
</dd></dl>

</section>
<section id="creating-network-servers">
<h3><a class="toc-backref" href="#id6">Creating network servers</a><a class="headerlink" href="#creating-network-servers" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.create_server">
coroutine loop.create_server(protocol_factory, host=None, port=None, *, family=socket.AF_UNSPEC, flags=socket.AI_PASSIVE, sock=None, backlog=100, ssl=None, reuse_address=None, reuse_port=None, ssl_handshake_timeout=None, start_serving=True)<a class="headerlink" href="#asyncio.loop.create_server" title="Permalink to this definition">¶</a></dt>
<dd>Create a TCP server (socket type <a class="reference internal" href="socket.html#socket.SOCK_STREAM" title="socket.SOCK_STREAM"><code class="xref py py-data docutils literal notranslate">SOCK_STREAM</code></a>) listening
on port of the host address.
Returns a <a class="reference internal" href="#asyncio.Server" title="asyncio.Server"><code class="xref py py-class docutils literal notranslate">Server</code></a> object.
Arguments:
<ul>
<li>protocol_factory must be a callable returning a
<a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">protocol</a> implementation.</li>
<li>The host parameter can be set to several types which determine where
the server would be listening:
<ul class="simple">
<li>If host is a string, the TCP server is bound to a single network
interface specified by host.</li>
<li>If host is a sequence of strings, the TCP server is bound to all
network interfaces specified by the sequence.</li>
<li>If host is an empty string or <code class="docutils literal notranslate">None</code>, all interfaces are
assumed and a list of multiple sockets will be returned (most likely
one for IPv4 and another one for IPv6).</li>
</ul>
</li>
<li>The port parameter can be set to specify which port the server should
listen on. If <code class="docutils literal notranslate">0</code> or <code class="docutils literal notranslate">None</code> (the default), a random unused port will
be selected (note that if host resolves to multiple network interfaces,
a different random port will be selected for each interface).</li>
<li>family can be set to either <a class="reference internal" href="socket.html#socket.AF_INET" title="socket.AF_INET"><code class="xref py py-data docutils literal notranslate">socket.AF_INET</code></a> or
<a class="reference internal" href="socket.html#socket.AF_INET6" title="socket.AF_INET6"><code class="xref py py-data docutils literal notranslate">AF_INET6</code></a> to force the socket to use IPv4 or IPv6.
If not set, the family will be determined from host name
(defaults to <code class="xref py py-data docutils literal notranslate">AF_UNSPEC</code>).</li>
<li>flags is a bitmask for <a class="reference internal" href="#asyncio.loop.getaddrinfo" title="asyncio.loop.getaddrinfo"><code class="xref py py-meth docutils literal notranslate">getaddrinfo()</code></a>.</li>
<li>sock can optionally be specified in order to use a preexisting
socket object. If specified, host and port must not be specified.
<div class="admonition note">
Note
The sock argument transfers ownership of the socket to the
server created. To close the socket, call the server’s
<a class="reference internal" href="#asyncio.Server.close" title="asyncio.Server.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a> method.
</div>
</li>
<li>backlog is the maximum number of queued connections passed to
<a class="reference internal" href="socket.html#socket.socket.listen" title="socket.socket.listen"><code class="xref py py-meth docutils literal notranslate">listen()</code></a> (defaults to 100).</li>
<li>ssl can be set to an <a class="reference internal" href="ssl.html#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate">SSLContext</code></a> instance to enable
TLS over the accepted connections.</li>
<li>reuse_address tells the kernel to reuse a local socket in
<code class="docutils literal notranslate">TIME_WAIT</code> state, without waiting for its natural timeout to
expire. If not specified will automatically be set to <code class="docutils literal notranslate">True</code> on
Unix.</li>
<li>reuse_port tells the kernel to allow this endpoint to be bound to the
same port as other existing endpoints are bound to, so long as they all
set this flag when being created. This option is not supported on
Windows.</li>
<li>ssl_handshake_timeout is (for a TLS server) the time in seconds to wait
for the TLS handshake to complete before aborting the connection.
<code class="docutils literal notranslate">60.0</code> seconds if <code class="docutils literal notranslate">None</code> (default).</li>
<li>start_serving set to <code class="docutils literal notranslate">True</code> (the default) causes the created server
to start accepting connections immediately. When set to <code class="docutils literal notranslate">False</code>,
the user should await on <a class="reference internal" href="#asyncio.Server.start_serving" title="asyncio.Server.start_serving"><code class="xref py py-meth docutils literal notranslate">Server.start_serving()</code></a> or
<a class="reference internal" href="#asyncio.Server.serve_forever" title="asyncio.Server.serve_forever"><code class="xref py py-meth docutils literal notranslate">Server.serve_forever()</code></a> to make the server to start accepting
connections.</li>
</ul>
<div class="versionchanged">
Changed in version 3.5: Added support for SSL/TLS in <a class="reference internal" href="#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate">ProactorEventLoop</code></a>.
</div>
<div class="versionchanged">
Changed in version 3.5.1: The host parameter can be a sequence of strings.
</div>
<div class="versionchanged">
Changed in version 3.6: Added ssl_handshake_timeout and start_serving parameters.
The socket option <code class="xref py py-data docutils literal notranslate">TCP_NODELAY</code> is set by default
for all TCP connections.
</div>
<div class="admonition seealso">
See also
The <a class="reference internal" href="asyncio-stream.html#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate">start_server()</code></a> function is a higher-level alternative API
that returns a pair of <a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate">StreamReader</code></a> and <a class="reference internal" href="asyncio-stream.html#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate">StreamWriter</code></a>
that can be used in an async/await code.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.create_unix_server">
coroutine loop.create_unix_server(protocol_factory, path=None, *, sock=None, backlog=100, ssl=None, ssl_handshake_timeout=None, start_serving=True)<a class="headerlink" href="#asyncio.loop.create_unix_server" title="Permalink to this definition">¶</a></dt>
<dd>Similar to <a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">loop.create_server()</code></a> but works with the
<a class="reference internal" href="socket.html#socket.AF_UNIX" title="socket.AF_UNIX"><code class="xref py py-data docutils literal notranslate">AF_UNIX</code></a> socket family.
path is the name of a Unix domain socket, and is required,
unless a sock argument is provided. Abstract Unix sockets,
<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>, <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a>, and <a class="reference internal" href="pathlib.html#pathlib.Path" title="pathlib.Path"><code class="xref py py-class docutils literal notranslate">Path</code></a> paths
are supported.
See the documentation of the <a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">loop.create_server()</code></a> method
for information about arguments to this method.
<a class="reference internal" href="intro.html#availability">Availability</a>: Unix.
<div class="versionchanged">
Changed in version 3.7: Added the ssl_handshake_timeout and start_serving parameters.
The path parameter can now be a <a class="reference internal" href="pathlib.html#pathlib.Path" title="pathlib.Path"><code class="xref py py-class docutils literal notranslate">Path</code></a> object.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.connect_accepted_socket">
coroutine loop.connect_accepted_socket(protocol_factory, sock, *, ssl=None, ssl_handshake_timeout=None)<a class="headerlink" href="#asyncio.loop.connect_accepted_socket" title="Permalink to this definition">¶</a></dt>
<dd>Wrap an already accepted connection into a transport/protocol pair.
This method can be used by servers that accept connections outside
of asyncio but that use asyncio to handle them.
Parameters:
<ul>
<li>protocol_factory must be a callable returning a
<a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">protocol</a> implementation.</li>
<li>sock is a preexisting socket object returned from
<a class="reference internal" href="socket.html#socket.socket.accept" title="socket.socket.accept"><code class="xref py py-meth docutils literal notranslate">socket.accept</code></a>.
<div class="admonition note">
Note
The sock argument transfers ownership of the socket to the
transport created. To close the socket, call the transport’s
<a class="reference internal" href="asyncio-protocol.html#asyncio.BaseTransport.close" title="asyncio.BaseTransport.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a> method.
</div>
</li>
<li>ssl can be set to an <a class="reference internal" href="ssl.html#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate">SSLContext</code></a> to enable SSL over
the accepted connections.</li>
<li>ssl_handshake_timeout is (for an SSL connection) the time in seconds to
wait for the SSL handshake to complete before aborting the connection.
<code class="docutils literal notranslate">60.0</code> seconds if <code class="docutils literal notranslate">None</code> (default).</li>
</ul>
Returns a <code class="docutils literal notranslate">(transport, protocol)</code> pair.
<div class="versionadded">
New in version 3.5.3.
</div>
<div class="versionchanged">
Changed in version 3.7: Added the ssl_handshake_timeout parameter.
</div>
</dd></dl>

</section>
<section id="transferring-files">
<h3><a class="toc-backref" href="#id7">Transferring files</a><a class="headerlink" href="#transferring-files" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.sendfile">
coroutine loop.sendfile(transport, file, offset=0, count=None, *, fallback=True)<a class="headerlink" href="#asyncio.loop.sendfile" title="Permalink to this definition">¶</a></dt>
<dd>Send a file over a transport. Return the total number of bytes
sent.
The method uses high-performance <a class="reference internal" href="os.html#os.sendfile" title="os.sendfile"><code class="xref py py-meth docutils literal notranslate">os.sendfile()</code></a> if available.
file must be a regular file object opened in binary mode.
offset tells from where to start reading the file. If specified,
count is the total number of bytes to transmit as opposed to
sending the file until EOF is reached. File position is always updated,
even when this method raises an error, and
<a class="reference internal" href="io.html#io.IOBase.tell" title="io.IOBase.tell"><code class="xref py py-meth docutils literal notranslate">file.tell()</code></a> can be used to obtain the actual
number of bytes sent.
fallback set to <code class="docutils literal notranslate">True</code> makes asyncio to manually read and send
the file when the platform does not support the sendfile system call
(e.g. Windows or SSL socket on Unix).
Raise <a class="reference internal" href="asyncio-exceptions.html#asyncio.SendfileNotAvailableError" title="asyncio.SendfileNotAvailableError"><code class="xref py py-exc docutils literal notranslate">SendfileNotAvailableError</code></a> if the system does not support
the sendfile syscall and fallback is <code class="docutils literal notranslate">False</code>.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

</section>
<section id="tls-upgrade">
<h3><a class="toc-backref" href="#id8">TLS Upgrade</a><a class="headerlink" href="#tls-upgrade" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.start_tls">
coroutine loop.start_tls(transport, protocol, sslcontext, *, server_side=False, server_hostname=None, ssl_handshake_timeout=None)<a class="headerlink" href="#asyncio.loop.start_tls" title="Permalink to this definition">¶</a></dt>
<dd>Upgrade an existing transport-based connection to TLS.
Create a TLS coder/decoder instance and insert it between the transport
and the protocol. The coder/decoder implements both transport-facing
protocol and protocol-facing transport.
Return the created two-interface instance. After await, the protocol
must stop using the original transport and communicate with the returned
object only because the coder caches protocol-side data and sporadically
exchanges extra TLS session packets with transport.
Parameters:
<ul class="simple">
<li>transport and protocol instances that methods like
<a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">create_server()</code></a> and
<a class="reference internal" href="#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate">create_connection()</code></a> return.</li>
<li>sslcontext: a configured instance of <a class="reference internal" href="ssl.html#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate">SSLContext</code></a>.</li>
<li>server_side pass <code class="docutils literal notranslate">True</code> when a server-side connection is being
upgraded (like the one created by <a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">create_server()</code></a>).</li>
<li>server_hostname: sets or overrides the host name that the target
server’s certificate will be matched against.</li>
<li>ssl_handshake_timeout is (for a TLS connection) the time in seconds to
wait for the TLS handshake to complete before aborting the connection.
<code class="docutils literal notranslate">60.0</code> seconds if <code class="docutils literal notranslate">None</code> (default).</li>
</ul>
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

</section>
<section id="watching-file-descriptors">
<h3><a class="toc-backref" href="#id9">Watching file descriptors</a><a class="headerlink" href="#watching-file-descriptors" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.add_reader">
loop.add_reader(fd, callback, *args)<a class="headerlink" href="#asyncio.loop.add_reader" title="Permalink to this definition">¶</a></dt>
<dd>Start monitoring the fd file descriptor for read availability and
invoke callback with the specified arguments once fd is available for
reading.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.remove_reader">
loop.remove_reader(fd)<a class="headerlink" href="#asyncio.loop.remove_reader" title="Permalink to this definition">¶</a></dt>
<dd>Stop monitoring the fd file descriptor for read availability. Returns
<code class="docutils literal notranslate">True</code> if fd was previously being monitored for reads.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.add_writer">
loop.add_writer(fd, callback, *args)<a class="headerlink" href="#asyncio.loop.add_writer" title="Permalink to this definition">¶</a></dt>
<dd>Start monitoring the fd file descriptor for write availability and
invoke callback with the specified arguments once fd is available for
writing.
Use <a class="reference internal" href="functools.html#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate">functools.partial()</code></a> <a class="reference internal" href="#asyncio-pass-keywords">to pass keyword arguments</a> to callback.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.remove_writer">
loop.remove_writer(fd)<a class="headerlink" href="#asyncio.loop.remove_writer" title="Permalink to this definition">¶</a></dt>
<dd>Stop monitoring the fd file descriptor for write availability. Returns
<code class="docutils literal notranslate">True</code> if fd was previously being monitored for writes.
</dd></dl>

See also <a class="reference internal" href="asyncio-platforms.html#asyncio-platform-support">Platform Support</a> section
for some limitations of these methods.
</section>
<section id="working-with-socket-objects-directly">
<h3><a class="toc-backref" href="#id10">Working with socket objects directly</a><a class="headerlink" href="#working-with-socket-objects-directly" title="Permalink to this headline">¶</a></h3>
In general, protocol implementations that use transport-based APIs
such as <a class="reference internal" href="#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate">loop.create_connection()</code></a> and <a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">loop.create_server()</code></a>
are faster than implementations that work with sockets directly.
However, there are some use cases when performance is not critical, and
working with <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate">socket</code></a> objects directly is more
convenient.
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.sock_recv">
coroutine loop.sock_recv(sock, nbytes)<a class="headerlink" href="#asyncio.loop.sock_recv" title="Permalink to this definition">¶</a></dt>
<dd>Receive up to nbytes from sock. Asynchronous version of
<a class="reference internal" href="socket.html#socket.socket.recv" title="socket.socket.recv"><code class="xref py py-meth docutils literal notranslate">socket.recv()</code></a>.
Return the received data as a bytes object.
sock must be a non-blocking socket.
<div class="versionchanged">
Changed in version 3.7: Even though this method was always documented as a coroutine
method, releases before Python 3.7 returned a <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">Future</code></a>.
Since Python 3.7 this is an <code class="docutils literal notranslate">async def</code> method.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.sock_recv_into">
coroutine loop.sock_recv_into(sock, buf)<a class="headerlink" href="#asyncio.loop.sock_recv_into" title="Permalink to this definition">¶</a></dt>
<dd>Receive data from sock into the buf buffer. Modeled after the blocking
<a class="reference internal" href="socket.html#socket.socket.recv_into" title="socket.socket.recv_into"><code class="xref py py-meth docutils literal notranslate">socket.recv_into()</code></a> method.
Return the number of bytes written to the buffer.
sock must be a non-blocking socket.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.sock_sendall">
coroutine loop.sock_sendall(sock, data)<a class="headerlink" href="#asyncio.loop.sock_sendall" title="Permalink to this definition">¶</a></dt>
<dd>Send data to the sock socket. Asynchronous version of
<a class="reference internal" href="socket.html#socket.socket.sendall" title="socket.socket.sendall"><code class="xref py py-meth docutils literal notranslate">socket.sendall()</code></a>.
This method continues to send to the socket until either all data
in data has been sent or an error occurs. <code class="docutils literal notranslate">None</code> is returned
on success. On error, an exception is raised. Additionally, there is no way
to determine how much data, if any, was successfully processed by the
receiving end of the connection.
sock must be a non-blocking socket.
<div class="versionchanged">
Changed in version 3.7: Even though the method was always documented as a coroutine
method, before Python 3.7 it returned an <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">Future</code></a>.
Since Python 3.7, this is an <code class="docutils literal notranslate">async def</code> method.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.sock_connect">
coroutine loop.sock_connect(sock, address)<a class="headerlink" href="#asyncio.loop.sock_connect" title="Permalink to this definition">¶</a></dt>
<dd>Connect sock to a remote socket at address.
Asynchronous version of <a class="reference internal" href="socket.html#socket.socket.connect" title="socket.socket.connect"><code class="xref py py-meth docutils literal notranslate">socket.connect()</code></a>.
sock must be a non-blocking socket.
<div class="versionchanged">
Changed in version 3.5.2: <code class="docutils literal notranslate">address</code> no longer needs to be resolved. <code class="docutils literal notranslate">sock_connect</code>
will try to check if the address is already resolved by calling
<a class="reference internal" href="socket.html#socket.inet_pton" title="socket.inet_pton"><code class="xref py py-func docutils literal notranslate">socket.inet_pton()</code></a>. If not,
<a class="reference internal" href="#asyncio.loop.getaddrinfo" title="asyncio.loop.getaddrinfo"><code class="xref py py-meth docutils literal notranslate">loop.getaddrinfo()</code></a> will be used to resolve the
address.
</div>
<div class="admonition seealso">
See also
<a class="reference internal" href="#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate">loop.create_connection()</code></a>
and <a class="reference internal" href="asyncio-stream.html#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate">asyncio.open_connection()</code></a>.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.sock_accept">
coroutine loop.sock_accept(sock)<a class="headerlink" href="#asyncio.loop.sock_accept" title="Permalink to this definition">¶</a></dt>
<dd>Accept a connection. Modeled after the blocking
<a class="reference internal" href="socket.html#socket.socket.accept" title="socket.socket.accept"><code class="xref py py-meth docutils literal notranslate">socket.accept()</code></a> method.
The socket must be bound to an address and listening
for connections. The return value is a pair <code class="docutils literal notranslate">(conn, address)</code> where conn
is a new socket object usable to send and receive data on the connection,
and address is the address bound to the socket on the other end of the
connection.
sock must be a non-blocking socket.
<div class="versionchanged">
Changed in version 3.7: Even though the method was always documented as a coroutine
method, before Python 3.7 it returned a <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">Future</code></a>.
Since Python 3.7, this is an <code class="docutils literal notranslate">async def</code> method.
</div>
<div class="admonition seealso">
See also
<a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">loop.create_server()</code></a> and <a class="reference internal" href="asyncio-stream.html#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate">start_server()</code></a>.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.sock_sendfile">
coroutine loop.sock_sendfile(sock, file, offset=0, count=None, *, fallback=True)<a class="headerlink" href="#asyncio.loop.sock_sendfile" title="Permalink to this definition">¶</a></dt>
<dd>Send a file using high-performance <a class="reference internal" href="os.html#os.sendfile" title="os.sendfile"><code class="xref py py-mod docutils literal notranslate">os.sendfile</code></a> if possible.
Return the total number of bytes sent.
Asynchronous version of <a class="reference internal" href="socket.html#socket.socket.sendfile" title="socket.socket.sendfile"><code class="xref py py-meth docutils literal notranslate">socket.sendfile()</code></a>.
sock must be a non-blocking <a class="reference internal" href="socket.html#socket.SOCK_STREAM" title="socket.SOCK_STREAM"><code class="xref py py-const docutils literal notranslate">socket.SOCK_STREAM</code></a>
<a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate">socket</code></a>.
file must be a regular file object open in binary mode.
offset tells from where to start reading the file. If specified,
count is the total number of bytes to transmit as opposed to
sending the file until EOF is reached. File position is always updated,
even when this method raises an error, and
<a class="reference internal" href="io.html#io.IOBase.tell" title="io.IOBase.tell"><code class="xref py py-meth docutils literal notranslate">file.tell()</code></a> can be used to obtain the actual
number of bytes sent.
fallback, when set to <code class="docutils literal notranslate">True</code>, makes asyncio manually read and send
the file when the platform does not support the sendfile syscall
(e.g. Windows or SSL socket on Unix).
Raise <a class="reference internal" href="asyncio-exceptions.html#asyncio.SendfileNotAvailableError" title="asyncio.SendfileNotAvailableError"><code class="xref py py-exc docutils literal notranslate">SendfileNotAvailableError</code></a> if the system does not support
sendfile syscall and fallback is <code class="docutils literal notranslate">False</code>.
sock must be a non-blocking socket.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

</section>
<section id="dns">
<h3><a class="toc-backref" href="#id11">DNS</a><a class="headerlink" href="#dns" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.getaddrinfo">
coroutine loop.getaddrinfo(host, port, *, family=0, type=0, proto=0, flags=0)<a class="headerlink" href="#asyncio.loop.getaddrinfo" title="Permalink to this definition">¶</a></dt>
<dd>Asynchronous version of <a class="reference internal" href="socket.html#socket.getaddrinfo" title="socket.getaddrinfo"><code class="xref py py-meth docutils literal notranslate">socket.getaddrinfo()</code></a>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.getnameinfo">
coroutine loop.getnameinfo(sockaddr, flags=0)<a class="headerlink" href="#asyncio.loop.getnameinfo" title="Permalink to this definition">¶</a></dt>
<dd>Asynchronous version of <a class="reference internal" href="socket.html#socket.getnameinfo" title="socket.getnameinfo"><code class="xref py py-meth docutils literal notranslate">socket.getnameinfo()</code></a>.
</dd></dl>

<div class="versionchanged">
Changed in version 3.7: Both getaddrinfo and getnameinfo methods were always documented
to return a coroutine, but prior to Python 3.7 they were, in fact,
returning <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">asyncio.Future</code></a> objects. Starting with Python 3.7
both methods are coroutines.
</div>
</section>
<section id="working-with-pipes">
<h3><a class="toc-backref" href="#id12">Working with pipes</a><a class="headerlink" href="#working-with-pipes" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.connect_read_pipe">
coroutine loop.connect_read_pipe(protocol_factory, pipe)<a class="headerlink" href="#asyncio.loop.connect_read_pipe" title="Permalink to this definition">¶</a></dt>
<dd>Register the read end of pipe in the event loop.
protocol_factory must be a callable returning an
<a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">asyncio protocol</a> implementation.
pipe is a <a class="reference internal" href="../glossary.html#term-file-object">file-like object</a>.
Return pair <code class="docutils literal notranslate">(transport, protocol)</code>, where transport supports
the <a class="reference internal" href="asyncio-protocol.html#asyncio.ReadTransport" title="asyncio.ReadTransport"><code class="xref py py-class docutils literal notranslate">ReadTransport</code></a> interface and protocol is an object
instantiated by the protocol_factory.
With <a class="reference internal" href="#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate">SelectorEventLoop</code></a> event loop, the pipe is set to
non-blocking mode.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.connect_write_pipe">
coroutine loop.connect_write_pipe(protocol_factory, pipe)<a class="headerlink" href="#asyncio.loop.connect_write_pipe" title="Permalink to this definition">¶</a></dt>
<dd>Register the write end of pipe in the event loop.
protocol_factory must be a callable returning an
<a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">asyncio protocol</a> implementation.
pipe is <a class="reference internal" href="../glossary.html#term-file-object">file-like object</a>.
Return pair <code class="docutils literal notranslate">(transport, protocol)</code>, where transport supports
<a class="reference internal" href="asyncio-protocol.html#asyncio.WriteTransport" title="asyncio.WriteTransport"><code class="xref py py-class docutils literal notranslate">WriteTransport</code></a> interface and protocol is an object
instantiated by the protocol_factory.
With <a class="reference internal" href="#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate">SelectorEventLoop</code></a> event loop, the pipe is set to
non-blocking mode.
</dd></dl>

<div class="admonition note">
Note
<a class="reference internal" href="#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate">SelectorEventLoop</code></a> does not support the above methods on
Windows. Use <a class="reference internal" href="#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate">ProactorEventLoop</code></a> instead for Windows.
</div>
<div class="admonition seealso">
See also
The <a class="reference internal" href="#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate">loop.subprocess_exec()</code></a> and
<a class="reference internal" href="#asyncio.loop.subprocess_shell" title="asyncio.loop.subprocess_shell"><code class="xref py py-meth docutils literal notranslate">loop.subprocess_shell()</code></a> methods.
</div>
</section>
<section id="unix-signals">
<h3><a class="toc-backref" href="#id13">Unix signals</a><a class="headerlink" href="#unix-signals" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.add_signal_handler">
loop.add_signal_handler(signum, callback, *args)<a class="headerlink" href="#asyncio.loop.add_signal_handler" title="Permalink to this definition">¶</a></dt>
<dd>Set callback as the handler for the signum signal.
The callback will be invoked by loop, along with other queued callbacks
and runnable coroutines of that event loop. Unlike signal handlers
registered using <a class="reference internal" href="signal.html#signal.signal" title="signal.signal"><code class="xref py py-func docutils literal notranslate">signal.signal()</code></a>, a callback registered with this
function is allowed to interact with the event loop.
Raise <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a> if the signal number is invalid or uncatchable.
Raise <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> if there is a problem setting up the handler.
Use <a class="reference internal" href="functools.html#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate">functools.partial()</code></a> <a class="reference internal" href="#asyncio-pass-keywords">to pass keyword arguments</a> to callback.
Like <a class="reference internal" href="signal.html#signal.signal" title="signal.signal"><code class="xref py py-func docutils literal notranslate">signal.signal()</code></a>, this function must be invoked in the main
thread.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.remove_signal_handler">
loop.remove_signal_handler(sig)<a class="headerlink" href="#asyncio.loop.remove_signal_handler" title="Permalink to this definition">¶</a></dt>
<dd>Remove the handler for the sig signal.
Return <code class="docutils literal notranslate">True</code> if the signal handler was removed, or <code class="docutils literal notranslate">False</code> if
no handler was set for the given signal.
<a class="reference internal" href="intro.html#availability">Availability</a>: Unix.
</dd></dl>

<div class="admonition seealso">
See also
The <a class="reference internal" href="signal.html#module-signal" title="signal: Set handlers for asynchronous events."><code class="xref py py-mod docutils literal notranslate">signal</code></a> module.
</div>
</section>
<section id="executing-code-in-thread-or-process-pools">
<h3><a class="toc-backref" href="#id14">Executing code in thread or process pools</a><a class="headerlink" href="#executing-code-in-thread-or-process-pools" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.run_in_executor">
awaitable loop.run_in_executor(executor, func, *args)<a class="headerlink" href="#asyncio.loop.run_in_executor" title="Permalink to this definition">¶</a></dt>
<dd>Arrange for func to be called in the specified executor.
The executor argument should be an <a class="reference internal" href="concurrent.futures.html#concurrent.futures.Executor" title="concurrent.futures.Executor"><code class="xref py py-class docutils literal notranslate">concurrent.futures.Executor</code></a>
instance. The default executor is used if executor is <code class="docutils literal notranslate">None</code>.
Example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import asyncio
import concurrent.futures

def blocking_io():
 # File operations (such as logging) can block the
 # event loop: run them in a thread pool.
 with open(&#39;/dev/urandom&#39;, &#39;rb&#39;) as f:
 return f.read(100)

def cpu_bound():
 # CPU-bound operations will block the event loop:
 # in general it is preferable to run them in a
 # process pool.
 return sum(i * i for i in range(10 ** 7))

async def main():
 loop = asyncio.get_running_loop()

## Options:

# 1. Run in the default loop&#39;s executor:
 result = await loop.run_in_executor(
 None, blocking_io)
 print(&#39;default thread pool&#39;, result)

# 2. Run in a custom thread pool:
 with concurrent.futures.ThreadPoolExecutor() as pool:
 result = await loop.run_in_executor(
 pool, blocking_io)
 print(&#39;custom thread pool&#39;, result)

# 3. Run in a custom process pool:
 with concurrent.futures.ProcessPoolExecutor() as pool:
 result = await loop.run_in_executor(
 pool, cpu_bound)
 print(&#39;custom process pool&#39;, result)

if __name__ == &#39;__main__&#39;:
 asyncio.run(main())
</pre></div>
</div>
Note that the entry point guard (<code class="docutils literal notranslate">if __name__ == '__main__'</code>)
is required for option 3 due to the peculiarities of <a class="reference internal" href="multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate">multiprocessing</code></a>,
which is used by <a class="reference internal" href="concurrent.futures.html#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate">ProcessPoolExecutor</code></a>.
See <a class="reference internal" href="multiprocessing.html#multiprocessing-safe-main-import">Safe importing of main module</a>.
This method returns a <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">asyncio.Future</code></a> object.
Use <a class="reference internal" href="functools.html#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate">functools.partial()</code></a> <a class="reference internal" href="#asyncio-pass-keywords">to pass keyword arguments</a> to func.
<div class="versionchanged">
Changed in version 3.5.3: <a class="reference internal" href="#asyncio.loop.run_in_executor" title="asyncio.loop.run_in_executor"><code class="xref py py-meth docutils literal notranslate">loop.run_in_executor()</code></a> no longer configures the
<code class="docutils literal notranslate">max_workers</code> of the thread pool executor it creates, instead
leaving it up to the thread pool executor
(<a class="reference internal" href="concurrent.futures.html#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate">ThreadPoolExecutor</code></a>) to set the
default.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.set_default_executor">
loop.set_default_executor(executor)<a class="headerlink" href="#asyncio.loop.set_default_executor" title="Permalink to this definition">¶</a></dt>
<dd>Set executor as the default executor used by <a class="reference internal" href="#asyncio.loop.run_in_executor" title="asyncio.loop.run_in_executor"><code class="xref py py-meth docutils literal notranslate">run_in_executor()</code></a>.
executor should be an instance of
<a class="reference internal" href="concurrent.futures.html#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate">ThreadPoolExecutor</code></a>.
<div class="deprecated">
Deprecated since version 3.8: Using an executor that is not an instance of
<a class="reference internal" href="concurrent.futures.html#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate">ThreadPoolExecutor</code></a> is deprecated and
will trigger an error in Python 3.9.
</div>
executor must be an instance of
<a class="reference internal" href="concurrent.futures.html#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-class docutils literal notranslate">concurrent.futures.ThreadPoolExecutor</code></a>.
</dd></dl>

</section>
<section id="error-handling-api">
<h3><a class="toc-backref" href="#id15">Error Handling API</a><a class="headerlink" href="#error-handling-api" title="Permalink to this headline">¶</a></h3>
Allows customizing how exceptions are handled in the event loop.
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.set_exception_handler">
loop.set_exception_handler(handler)<a class="headerlink" href="#asyncio.loop.set_exception_handler" title="Permalink to this definition">¶</a></dt>
<dd>Set handler as the new event loop exception handler.
If handler is <code class="docutils literal notranslate">None</code>, the default exception handler will
be set. Otherwise, handler must be a callable with the signature
matching <code class="docutils literal notranslate">(loop, context)</code>, where <code class="docutils literal notranslate">loop</code>
is a reference to the active event loop, and <code class="docutils literal notranslate">context</code>
is a <code class="docutils literal notranslate">dict</code> object containing the details of the exception
(see <a class="reference internal" href="#asyncio.loop.call_exception_handler" title="asyncio.loop.call_exception_handler"><code class="xref py py-meth docutils literal notranslate">call_exception_handler()</code></a> documentation for details
about context).
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.get_exception_handler">
loop.get_exception_handler()<a class="headerlink" href="#asyncio.loop.get_exception_handler" title="Permalink to this definition">¶</a></dt>
<dd>Return the current exception handler, or <code class="docutils literal notranslate">None</code> if no custom
exception handler was set.
<div class="versionadded">
New in version 3.5.2.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.default_exception_handler">
loop.default_exception_handler(context)<a class="headerlink" href="#asyncio.loop.default_exception_handler" title="Permalink to this definition">¶</a></dt>
<dd>Default exception handler.
This is called when an exception occurs and no exception
handler is set. This can be called by a custom exception
handler that wants to defer to the default handler behavior.
context parameter has the same meaning as in
<a class="reference internal" href="#asyncio.loop.call_exception_handler" title="asyncio.loop.call_exception_handler"><code class="xref py py-meth docutils literal notranslate">call_exception_handler()</code></a>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.call_exception_handler">
loop.call_exception_handler(context)<a class="headerlink" href="#asyncio.loop.call_exception_handler" title="Permalink to this definition">¶</a></dt>
<dd>Call the current event loop exception handler.
context is a <code class="docutils literal notranslate">dict</code> object containing the following keys
(new keys may be introduced in future Python versions):
<ul class="simple">
<li>‘message’: Error message;</li>
<li>‘exception’ (optional): Exception object;</li>
<li>‘future’ (optional): <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">asyncio.Future</code></a> instance;</li>
<li>‘task’ (optional): <a class="reference internal" href="asyncio-task.html#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate">asyncio.Task</code></a> instance;</li>
<li>‘handle’ (optional): <a class="reference internal" href="#asyncio.Handle" title="asyncio.Handle"><code class="xref py py-class docutils literal notranslate">asyncio.Handle</code></a> instance;</li>
<li>‘protocol’ (optional): <a class="reference internal" href="asyncio-protocol.html#asyncio-protocol">Protocol</a> instance;</li>
<li>‘transport’ (optional): <a class="reference internal" href="asyncio-protocol.html#asyncio-transport">Transport</a> instance;</li>
<li>‘socket’ (optional): <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate">socket.socket</code></a> instance;</li>
<li><dl class="simple">
<dt>‘asyncgen’ (optional): Asynchronous generator that caused</dt><dd>the exception.
</dd>
</dl>
</li>
</ul>
<div class="admonition note">
Note
This method should not be overloaded in subclassed
event loops. For custom exception handling, use
the <a class="reference internal" href="#asyncio.loop.set_exception_handler" title="asyncio.loop.set_exception_handler"><code class="xref py py-meth docutils literal notranslate">set_exception_handler()</code></a> method.
</div>
</dd></dl>

</section>
<section id="enabling-debug-mode">
<h3><a class="toc-backref" href="#id16">Enabling debug mode</a><a class="headerlink" href="#enabling-debug-mode" title="Permalink to this headline">¶</a></h3>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.get_debug">
loop.get_debug()<a class="headerlink" href="#asyncio.loop.get_debug" title="Permalink to this definition">¶</a></dt>
<dd>Get the debug mode (<a class="reference internal" href="functions.html#bool" title="bool"><code class="xref py py-class docutils literal notranslate">bool</code></a>) of the event loop.
The default value is <code class="docutils literal notranslate">True</code> if the environment variable
<a class="reference internal" href="../using/cmdline.html#envvar-PYTHONASYNCIODEBUG"><code class="xref std std-envvar docutils literal notranslate">PYTHONASYNCIODEBUG</code></a> is set to a non-empty string, <code class="docutils literal notranslate">False</code>
otherwise.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.set_debug">
loop.set_debug(enabled: <a class="reference internal" href="functions.html#bool" title="bool">bool</a>)<a class="headerlink" href="#asyncio.loop.set_debug" title="Permalink to this definition">¶</a></dt>
<dd>Set the debug mode of the event loop.
<div class="versionchanged">
Changed in version 3.7: The new <a class="reference internal" href="devmode.html#devmode">Python Development Mode</a> can now also be used
to enable the debug mode.
</div>
</dd></dl>

<div class="admonition seealso">
See also
The <a class="reference internal" href="asyncio-dev.html#asyncio-debug-mode">debug mode of asyncio</a>.
</div>
</section>
<section id="running-subprocesses">
<h3><a class="toc-backref" href="#id17">Running Subprocesses</a><a class="headerlink" href="#running-subprocesses" title="Permalink to this headline">¶</a></h3>
Methods described in this subsections are low-level. In regular
async/await code consider using the high-level
<a class="reference internal" href="asyncio-subprocess.html#asyncio.create_subprocess_shell" title="asyncio.create_subprocess_shell"><code class="xref py py-func docutils literal notranslate">asyncio.create_subprocess_shell()</code></a> and
<a class="reference internal" href="asyncio-subprocess.html#asyncio.create_subprocess_exec" title="asyncio.create_subprocess_exec"><code class="xref py py-func docutils literal notranslate">asyncio.create_subprocess_exec()</code></a> convenience functions instead.
<div class="admonition note">
Note
On Windows, the default event loop <a class="reference internal" href="#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate">ProactorEventLoop</code></a> supports
subprocesses, whereas <a class="reference internal" href="#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate">SelectorEventLoop</code></a> does not. See
<a class="reference internal" href="asyncio-platforms.html#asyncio-windows-subprocess">Subprocess Support on Windows</a> for
details.
</div>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.subprocess_exec">
coroutine loop.subprocess_exec(protocol_factory, *args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, **kwargs)<a class="headerlink" href="#asyncio.loop.subprocess_exec" title="Permalink to this definition">¶</a></dt>
<dd>Create a subprocess from one or more string arguments specified by
args.
args must be a list of strings represented by:
<ul class="simple">
<li><a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>;</li>
<li>or <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a>, encoded to the
<a class="reference internal" href="os.html#filesystem-encoding">filesystem encoding</a>.</li>
</ul>
The first string specifies the program executable,
and the remaining strings specify the arguments. Together, string
arguments form the <code class="docutils literal notranslate">argv</code> of the program.
This is similar to the standard library <a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal notranslate">subprocess.Popen</code></a>
class called with <code class="docutils literal notranslate">shell=False</code> and the list of strings passed as
the first argument; however, where <a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal notranslate">Popen</code></a> takes
a single argument which is list of strings, subprocess_exec
takes multiple string arguments.
The protocol_factory must be a callable returning a subclass of the
<a class="reference internal" href="asyncio-protocol.html#asyncio.SubprocessProtocol" title="asyncio.SubprocessProtocol"><code class="xref py py-class docutils literal notranslate">asyncio.SubprocessProtocol</code></a> class.
Other parameters:
<ul>
<li>stdin can be any of these:
<ul class="simple">
<li>a file-like object representing a pipe to be connected to the
subprocess’s standard input stream using
<a class="reference internal" href="#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate">connect_write_pipe()</code></a></li>
<li>the <a class="reference internal" href="subprocess.html#subprocess.PIPE" title="subprocess.PIPE"><code class="xref py py-const docutils literal notranslate">subprocess.PIPE</code></a> constant (default) which will create a new
pipe and connect it,</li>
<li>the value <code class="docutils literal notranslate">None</code> which will make the subprocess inherit the file
descriptor from this process</li>
<li>the <a class="reference internal" href="subprocess.html#subprocess.DEVNULL" title="subprocess.DEVNULL"><code class="xref py py-const docutils literal notranslate">subprocess.DEVNULL</code></a> constant which indicates that the
special <a class="reference internal" href="os.html#os.devnull" title="os.devnull"><code class="xref py py-data docutils literal notranslate">os.devnull</code></a> file will be used</li>
</ul>
</li>
<li>stdout can be any of these:
<ul class="simple">
<li>a file-like object representing a pipe to be connected to the
subprocess’s standard output stream using
<a class="reference internal" href="#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate">connect_write_pipe()</code></a></li>
<li>the <a class="reference internal" href="subprocess.html#subprocess.PIPE" title="subprocess.PIPE"><code class="xref py py-const docutils literal notranslate">subprocess.PIPE</code></a> constant (default) which will create a new
pipe and connect it,</li>
<li>the value <code class="docutils literal notranslate">None</code> which will make the subprocess inherit the file
descriptor from this process</li>
<li>the <a class="reference internal" href="subprocess.html#subprocess.DEVNULL" title="subprocess.DEVNULL"><code class="xref py py-const docutils literal notranslate">subprocess.DEVNULL</code></a> constant which indicates that the
special <a class="reference internal" href="os.html#os.devnull" title="os.devnull"><code class="xref py py-data docutils literal notranslate">os.devnull</code></a> file will be used</li>
</ul>
</li>
<li>stderr can be any of these:
<ul class="simple">
<li>a file-like object representing a pipe to be connected to the
subprocess’s standard error stream using
<a class="reference internal" href="#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate">connect_write_pipe()</code></a></li>
<li>the <a class="reference internal" href="subprocess.html#subprocess.PIPE" title="subprocess.PIPE"><code class="xref py py-const docutils literal notranslate">subprocess.PIPE</code></a> constant (default) which will create a new
pipe and connect it,</li>
<li>the value <code class="docutils literal notranslate">None</code> which will make the subprocess inherit the file
descriptor from this process</li>
<li>the <a class="reference internal" href="subprocess.html#subprocess.DEVNULL" title="subprocess.DEVNULL"><code class="xref py py-const docutils literal notranslate">subprocess.DEVNULL</code></a> constant which indicates that the
special <a class="reference internal" href="os.html#os.devnull" title="os.devnull"><code class="xref py py-data docutils literal notranslate">os.devnull</code></a> file will be used</li>
<li>the <a class="reference internal" href="subprocess.html#subprocess.STDOUT" title="subprocess.STDOUT"><code class="xref py py-const docutils literal notranslate">subprocess.STDOUT</code></a> constant which will connect the standard
error stream to the process’ standard output stream</li>
</ul>
</li>
<li>All other keyword arguments are passed to <a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal notranslate">subprocess.Popen</code></a>
without interpretation, except for bufsize, universal_newlines,
shell, text, encoding and errors, which should not be specified
at all.
The <code class="docutils literal notranslate">asyncio</code> subprocess API does not support decoding the streams
as text. <a class="reference internal" href="stdtypes.html#bytes.decode" title="bytes.decode"><code class="xref py py-func docutils literal notranslate">bytes.decode()</code></a> can be used to convert the bytes returned
from the stream to text.
</li>
</ul>
See the constructor of the <a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal notranslate">subprocess.Popen</code></a> class
for documentation on other arguments.
Returns a pair of <code class="docutils literal notranslate">(transport, protocol)</code>, where transport
conforms to the <a class="reference internal" href="asyncio-protocol.html#asyncio.SubprocessTransport" title="asyncio.SubprocessTransport"><code class="xref py py-class docutils literal notranslate">asyncio.SubprocessTransport</code></a> base class and
protocol is an object instantiated by the protocol_factory.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.loop.subprocess_shell">
coroutine loop.subprocess_shell(protocol_factory, cmd, *, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, **kwargs)<a class="headerlink" href="#asyncio.loop.subprocess_shell" title="Permalink to this definition">¶</a></dt>
<dd>Create a subprocess from cmd, which can be a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> or a
<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> string encoded to the
<a class="reference internal" href="os.html#filesystem-encoding">filesystem encoding</a>,
using the platform’s “shell” syntax.
This is similar to the standard library <a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal notranslate">subprocess.Popen</code></a>
class called with <code class="docutils literal notranslate">shell=True</code>.
The protocol_factory must be a callable returning a subclass of the
<a class="reference internal" href="asyncio-protocol.html#asyncio.SubprocessProtocol" title="asyncio.SubprocessProtocol"><code class="xref py py-class docutils literal notranslate">SubprocessProtocol</code></a> class.
See <a class="reference internal" href="#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate">subprocess_exec()</code></a> for more details about
the remaining arguments.
Returns a pair of <code class="docutils literal notranslate">(transport, protocol)</code>, where transport
conforms to the <a class="reference internal" href="asyncio-protocol.html#asyncio.SubprocessTransport" title="asyncio.SubprocessTransport"><code class="xref py py-class docutils literal notranslate">SubprocessTransport</code></a> base class and
protocol is an object instantiated by the protocol_factory.
</dd></dl>

<div class="admonition note">
Note
It is the application’s responsibility to ensure that all whitespace
and special characters are quoted appropriately to avoid <a class="reference external" href="https://en.wikipedia.org/wiki/Shell_injection#Shell_injection">shell injection</a>
vulnerabilities. The <a class="reference internal" href="shlex.html#shlex.quote" title="shlex.quote"><code class="xref py py-func docutils literal notranslate">shlex.quote()</code></a> function can be used to
properly escape whitespace and special characters in strings that
are going to be used to construct shell commands.
</div>
</section>
</section>
<section id="callback-handles">
<h2>Callback Handles<a class="headerlink" href="#callback-handles" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.Handle">
class asyncio.Handle<a class="headerlink" href="#asyncio.Handle" title="Permalink to this definition">¶</a></dt>
<dd>A callback wrapper object returned by <a class="reference internal" href="#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate">loop.call_soon()</code></a>,
<a class="reference internal" href="#asyncio.loop.call_soon_threadsafe" title="asyncio.loop.call_soon_threadsafe"><code class="xref py py-meth docutils literal notranslate">loop.call_soon_threadsafe()</code></a>.
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Handle.cancel">
cancel()<a class="headerlink" href="#asyncio.Handle.cancel" title="Permalink to this definition">¶</a></dt>
<dd>Cancel the callback. If the callback has already been canceled
or executed, this method has no effect.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Handle.cancelled">
cancelled()<a class="headerlink" href="#asyncio.Handle.cancelled" title="Permalink to this definition">¶</a></dt>
<dd>Return <code class="docutils literal notranslate">True</code> if the callback was cancelled.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="asyncio.TimerHandle">
class asyncio.TimerHandle<a class="headerlink" href="#asyncio.TimerHandle" title="Permalink to this definition">¶</a></dt>
<dd>A callback wrapper object returned by <a class="reference internal" href="#asyncio.loop.call_later" title="asyncio.loop.call_later"><code class="xref py py-meth docutils literal notranslate">loop.call_later()</code></a>,
and <a class="reference internal" href="#asyncio.loop.call_at" title="asyncio.loop.call_at"><code class="xref py py-meth docutils literal notranslate">loop.call_at()</code></a>.
This class is a subclass of <a class="reference internal" href="#asyncio.Handle" title="asyncio.Handle"><code class="xref py py-class docutils literal notranslate">Handle</code></a>.
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.TimerHandle.when">
when()<a class="headerlink" href="#asyncio.TimerHandle.when" title="Permalink to this definition">¶</a></dt>
<dd>Return a scheduled callback time as <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a> seconds.
The time is an absolute timestamp, using the same time
reference as <a class="reference internal" href="#asyncio.loop.time" title="asyncio.loop.time"><code class="xref py py-meth docutils literal notranslate">loop.time()</code></a>.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

</dd></dl>

</section>
<section id="server-objects">
<h2>Server Objects<a class="headerlink" href="#server-objects" title="Permalink to this headline">¶</a></h2>
Server objects are created by <a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">loop.create_server()</code></a>,
<a class="reference internal" href="#asyncio.loop.create_unix_server" title="asyncio.loop.create_unix_server"><code class="xref py py-meth docutils literal notranslate">loop.create_unix_server()</code></a>, <a class="reference internal" href="asyncio-stream.html#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate">start_server()</code></a>,
and <a class="reference internal" href="asyncio-stream.html#asyncio.start_unix_server" title="asyncio.start_unix_server"><code class="xref py py-func docutils literal notranslate">start_unix_server()</code></a> functions.
Do not instantiate the class directly.
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.Server">
class asyncio.Server<a class="headerlink" href="#asyncio.Server" title="Permalink to this definition">¶</a></dt>
<dd>Server objects are asynchronous context managers. When used in an
<code class="docutils literal notranslate">async with</code> statement, it’s guaranteed that the Server object is
closed and not accepting new connections when the <code class="docutils literal notranslate">async with</code>
statement is completed:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>srv = await loop.create_server(...)

async with srv:
 # some code

# At this point, srv is closed and no longer accepts new connections.
</pre></div>
</div>
<div class="versionchanged">
Changed in version 3.7: Server object is an asynchronous context manager since Python 3.7.
</div>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Server.close">
close()<a class="headerlink" href="#asyncio.Server.close" title="Permalink to this definition">¶</a></dt>
<dd>Stop serving: close listening sockets and set the <a class="reference internal" href="#asyncio.Server.sockets" title="asyncio.Server.sockets"><code class="xref py py-attr docutils literal notranslate">sockets</code></a>
attribute to <code class="docutils literal notranslate">None</code>.
The sockets that represent existing incoming client connections
are left open.
The server is closed asynchronously, use the <a class="reference internal" href="#asyncio.Server.wait_closed" title="asyncio.Server.wait_closed"><code class="xref py py-meth docutils literal notranslate">wait_closed()</code></a>
coroutine to wait until the server is closed.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Server.get_loop">
get_loop()<a class="headerlink" href="#asyncio.Server.get_loop" title="Permalink to this definition">¶</a></dt>
<dd>Return the event loop associated with the server object.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Server.start_serving">
coroutine start_serving()<a class="headerlink" href="#asyncio.Server.start_serving" title="Permalink to this definition">¶</a></dt>
<dd>Start accepting connections.
This method is idempotent, so it can be called when
the server is already being serving.
The start_serving keyword-only parameter to
<a class="reference internal" href="#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate">loop.create_server()</code></a> and
<a class="reference internal" href="asyncio-stream.html#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-meth docutils literal notranslate">asyncio.start_server()</code></a> allows creating a Server object
that is not accepting connections initially. In this case
<code class="docutils literal notranslate">Server.start_serving()</code>, or <a class="reference internal" href="#asyncio.Server.serve_forever" title="asyncio.Server.serve_forever"><code class="xref py py-meth docutils literal notranslate">Server.serve_forever()</code></a> can be used
to make the Server start accepting connections.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Server.serve_forever">
coroutine serve_forever()<a class="headerlink" href="#asyncio.Server.serve_forever" title="Permalink to this definition">¶</a></dt>
<dd>Start accepting connections until the coroutine is cancelled.
Cancellation of <code class="docutils literal notranslate">serve_forever</code> task causes the server
to be closed.
This method can be called if the server is already accepting
connections. Only one <code class="docutils literal notranslate">serve_forever</code> task can exist per
one Server object.
Example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>async def client_connected(reader, writer):
 # Communicate with the client with
 # reader/writer streams. For example:
 await reader.readline()

async def main(host, port):
 srv = await asyncio.start_server(
 client_connected, host, port)
 await srv.serve_forever()

asyncio.run(main(&#39;127.0.0.1&#39;, 0))
</pre></div>
</div>
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Server.is_serving">
is_serving()<a class="headerlink" href="#asyncio.Server.is_serving" title="Permalink to this definition">¶</a></dt>
<dd>Return <code class="docutils literal notranslate">True</code> if the server is accepting new connections.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Server.wait_closed">
coroutine wait_closed()<a class="headerlink" href="#asyncio.Server.wait_closed" title="Permalink to this definition">¶</a></dt>
<dd>Wait until the <a class="reference internal" href="#asyncio.Server.close" title="asyncio.Server.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a> method completes.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="asyncio.Server.sockets">
sockets<a class="headerlink" href="#asyncio.Server.sockets" title="Permalink to this definition">¶</a></dt>
<dd>List of <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate">socket.socket</code></a> objects the server is listening on.
<div class="versionchanged">
Changed in version 3.7: Prior to Python 3.7 <code class="docutils literal notranslate">Server.sockets</code> used to return an
internal list of server sockets directly. In 3.7 a copy
of that list is returned.
</div>
</dd></dl>

</dd></dl>

</section>
<section id="event-loop-implementations">
<h2>Event Loop Implementations<a class="headerlink" href="#event-loop-implementations" title="Permalink to this headline">¶</a></h2>
asyncio ships with two different event loop implementations:
<a class="reference internal" href="#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate">SelectorEventLoop</code></a> and <a class="reference internal" href="#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate">ProactorEventLoop</code></a>.
By default asyncio is configured to use <a class="reference internal" href="#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate">SelectorEventLoop</code></a>
on Unix and <a class="reference internal" href="#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate">ProactorEventLoop</code></a> on Windows.
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.SelectorEventLoop">
class asyncio.SelectorEventLoop<a class="headerlink" href="#asyncio.SelectorEventLoop" title="Permalink to this definition">¶</a></dt>
<dd>An event loop based on the <a class="reference internal" href="selectors.html#module-selectors" title="selectors: High-level I/O multiplexing."><code class="xref py py-mod docutils literal notranslate">selectors</code></a> module.
Uses the most efficient selector available for the given
platform. It is also possible to manually configure the
exact selector implementation to be used:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import asyncio
import selectors

class MyPolicy(asyncio.DefaultEventLoopPolicy):
 def new_event_loop(self):
 selector = selectors.SelectSelector()
 return asyncio.SelectorEventLoop(selector)

asyncio.set_event_loop_policy(MyPolicy())
</pre></div>
</div>
<a class="reference internal" href="intro.html#availability">Availability</a>: Unix, Windows.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="asyncio.ProactorEventLoop">
class asyncio.ProactorEventLoop<a class="headerlink" href="#asyncio.ProactorEventLoop" title="Permalink to this definition">¶</a></dt>
<dd>An event loop for Windows that uses “I/O Completion Ports” (IOCP).
<a class="reference internal" href="intro.html#availability">Availability</a>: Windows.
<div class="admonition seealso">
See also
<a class="reference external" href="https://docs.microsoft.com/en-ca/windows/desktop/FileIO/i-o-completion-ports">MSDN documentation on I/O Completion Ports</a>.
</div>
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="asyncio.AbstractEventLoop">
class asyncio.AbstractEventLoop<a class="headerlink" href="#asyncio.AbstractEventLoop" title="Permalink to this definition">¶</a></dt>
<dd>Abstract base class for asyncio-compliant event loops.
The <a class="reference internal" href="#asyncio-event-loop-methods">Event Loop Methods</a> section lists all
methods that an alternative implementation of <code class="docutils literal notranslate">AbstractEventLoop</code>
should have defined.
</dd></dl>

</section>
<section id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
Note that all examples in this section purposefully show how
to use the low-level event loop APIs, such as <a class="reference internal" href="#asyncio.loop.run_forever" title="asyncio.loop.run_forever"><code class="xref py py-meth docutils literal notranslate">loop.run_forever()</code></a>
and <a class="reference internal" href="#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate">loop.call_soon()</code></a>. Modern asyncio applications rarely
need to be written this way; consider using the high-level functions
like <a class="reference internal" href="asyncio-task.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate">asyncio.run()</code></a>.
<section id="hello-world-with-call-soon">
<h3>Hello World with call_soon()<a class="headerlink" href="#hello-world-with-call-soon" title="Permalink to this headline">¶</a></h3>
An example using the <a class="reference internal" href="#asyncio.loop.call_soon" title="asyncio.loop.call_soon"><code class="xref py py-meth docutils literal notranslate">loop.call_soon()</code></a> method to schedule a
callback. The callback displays <code class="docutils literal notranslate">&quot;Hello World&quot;</code> and then stops the
event loop:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import asyncio

def hello_world(loop):
 &quot;&quot;&quot;A callback to print &#39;Hello World&#39; and stop the event loop&quot;&quot;&quot;
 print(&#39;Hello World&#39;)
 loop.stop()

loop = asyncio.get_event_loop()

# Schedule a call to hello_world()
loop.call_soon(hello_world, loop)

# Blocking call interrupted by loop.stop()
try:
 loop.run_forever()
finally:
 loop.close()
</pre></div>
</div>
<div class="admonition seealso">
See also
A similar <a class="reference internal" href="asyncio-task.html#coroutine">Hello World</a>
example created with a coroutine and the <a class="reference internal" href="asyncio-task.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate">run()</code></a> function.
</div>
</section>
<section id="display-the-current-date-with-call-later">
<h3>Display the current date with call_later()<a class="headerlink" href="#display-the-current-date-with-call-later" title="Permalink to this headline">¶</a></h3>
An example of a callback displaying the current date every second. The
callback uses the <a class="reference internal" href="#asyncio.loop.call_later" title="asyncio.loop.call_later"><code class="xref py py-meth docutils literal notranslate">loop.call_later()</code></a> method to reschedule itself
after 5 seconds, and then stops the event loop:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import asyncio
import datetime

def display_date(end_time, loop):
 print(datetime.datetime.now())
 if (loop.time() + 1.0) &lt; end_time:
 loop.call_later(1, display_date, end_time, loop)
 else:
 loop.stop()

loop = asyncio.get_event_loop()

# Schedule the first call to display_date()
end_time = loop.time() + 5.0
loop.call_soon(display_date, end_time, loop)

# Blocking call interrupted by loop.stop()
try:
 loop.run_forever()
finally:
 loop.close()
</pre></div>
</div>
<div class="admonition seealso">
See also
A similar <a class="reference internal" href="asyncio-task.html#asyncio-example-sleep">current date</a> example
created with a coroutine and the <a class="reference internal" href="asyncio-task.html#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate">run()</code></a> function.
</div>
</section>
<section id="watch-a-file-descriptor-for-read-events">
<h3>Watch a file descriptor for read events<a class="headerlink" href="#watch-a-file-descriptor-for-read-events" title="Permalink to this headline">¶</a></h3>
Wait until a file descriptor received some data using the
<a class="reference internal" href="#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate">loop.add_reader()</code></a> method and then close the event loop:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import asyncio
from socket import socketpair

# Create a pair of connected file descriptors
rsock, wsock = socketpair()

loop = asyncio.get_event_loop()

def reader():
 data = rsock.recv(100)
 print(&quot;Received:&quot;, data.decode())

# We are done: unregister the file descriptor
 loop.remove_reader(rsock)

# Stop the event loop
 loop.stop()

# Register the file descriptor for read event
loop.add_reader(rsock, reader)

# Simulate the reception of data from the network
loop.call_soon(wsock.send, &#39;abc&#39;.encode())

try:
 # Run the event loop
 loop.run_forever()
finally:
 # We are done. Close sockets and the event loop.
 rsock.close()
 wsock.close()
 loop.close()
</pre></div>
</div>
<div class="admonition seealso">
See also
<ul class="simple">
<li>A similar <a class="reference internal" href="asyncio-protocol.html#asyncio-example-create-connection">example</a>
using transports, protocols, and the
<a class="reference internal" href="#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate">loop.create_connection()</code></a> method.</li>
<li>Another similar <a class="reference internal" href="asyncio-stream.html#asyncio-example-create-connection-streams">example</a>
using the high-level <a class="reference internal" href="asyncio-stream.html#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate">asyncio.open_connection()</code></a> function
and streams.</li>
</ul>
</div>
</section>
<section id="set-signal-handlers-for-sigint-and-sigterm">
<h3>Set signal handlers for SIGINT and SIGTERM<a class="headerlink" href="#set-signal-handlers-for-sigint-and-sigterm" title="Permalink to this headline">¶</a></h3>
(This <code class="docutils literal notranslate">signals</code> example only works on Unix.)
Register handlers for signals <code class="xref py py-data docutils literal notranslate">SIGINT</code> and <code class="xref py py-data docutils literal notranslate">SIGTERM</code>
using the <a class="reference internal" href="#asyncio.loop.add_signal_handler" title="asyncio.loop.add_signal_handler"><code class="xref py py-meth docutils literal notranslate">loop.add_signal_handler()</code></a> method:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>import asyncio
import functools
import os
import signal

def ask_exit(signame, loop):
 print(&quot;got signal %s: exit&quot; % signame)
 loop.stop()

for signame in {&#39;SIGINT&#39;, &#39;SIGTERM&#39;}:
 loop.add_signal_handler(
 getattr(signal, signame),
 functools.partial(ask_exit, signame, loop))

await asyncio.sleep(3600)

print(&quot;Event loop running for 1 hour, press Ctrl+C to interrupt.&quot;)
print(f&quot;pid {os.getpid()}: send SIGINT or SIGTERM to exit.&quot;)

asyncio.run(main())
</pre></div>
</div>
</section>
</section>
</section>

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 <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="#">Event Loop</a><ul>
<li><a class="reference internal" href="#event-loop-methods">Event Loop Methods</a><ul>
<li><a class="reference internal" href="#running-and-stopping-the-loop">Running and stopping the loop</a></li>
<li><a class="reference internal" href="#scheduling-callbacks">Scheduling callbacks</a></li>
<li><a class="reference internal" href="#scheduling-delayed-callbacks">Scheduling delayed callbacks</a></li>
<li><a class="reference internal" href="#creating-futures-and-tasks">Creating Futures and Tasks</a></li>
<li><a class="reference internal" href="#opening-network-connections">Opening network connections</a></li>
<li><a class="reference internal" href="#creating-network-servers">Creating network servers</a></li>
<li><a class="reference internal" href="#transferring-files">Transferring files</a></li>
<li><a class="reference internal" href="#tls-upgrade">TLS Upgrade</a></li>
<li><a class="reference internal" href="#watching-file-descriptors">Watching file descriptors</a></li>
<li><a class="reference internal" href="#working-with-socket-objects-directly">Working with socket objects directly</a></li>
<li><a class="reference internal" href="#dns">DNS</a></li>
<li><a class="reference internal" href="#working-with-pipes">Working with pipes</a></li>
<li><a class="reference internal" href="#unix-signals">Unix signals</a></li>
<li><a class="reference internal" href="#executing-code-in-thread-or-process-pools">Executing code in thread or process pools</a></li>
<li><a class="reference internal" href="#error-handling-api">Error Handling API</a></li>
<li><a class="reference internal" href="#enabling-debug-mode">Enabling debug mode</a></li>
<li><a class="reference internal" href="#running-subprocesses">Running Subprocesses</a></li>
</ul>
</li>
<li><a class="reference internal" href="#callback-handles">Callback Handles</a></li>
<li><a class="reference internal" href="#server-objects">Server Objects</a></li>
<li><a class="reference internal" href="#event-loop-implementations">Event Loop Implementations</a></li>
<li><a class="reference internal" href="#examples">Examples</a><ul>
<li><a class="reference internal" href="#hello-world-with-call-soon">Hello World with call_soon()</a></li>
<li><a class="reference internal" href="#display-the-current-date-with-call-later">Display the current date with call_later()</a></li>
<li><a class="reference internal" href="#watch-a-file-descriptor-for-read-events">Watch a file descriptor for read events</a></li>
<li><a class="reference internal" href="#set-signal-handlers-for-sigint-and-sigterm">Set signal handlers for SIGINT and SIGTERM</a></li>
</ul>
</li>
</ul>
</li>
</ul>

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