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:mod:`asyncio` -- Asynchronous I/O, event loop, coroutines and tasks
====================================================================
.. module:: asyncio
:synopsis: Asynchronous I/O, event loop, coroutines and tasks.
.. note::
The asyncio package has been included in the standard library on a
:term:`provisional basis <provisional package>`. Backwards incompatible
changes (up to and including removal of the module) may occur if deemed
necessary by the core developers.
.. versionadded:: 3.4
**Source code:** :source:`Lib/asyncio/`
--------------
This module provides infrastructure for writing single-threaded concurrent
code using coroutines, multiplexing I/O access over sockets and other
resources, running network clients and servers, and other related primitives.
Here is a more detailed list of the package contents:
* a pluggable :ref:`event loop <asyncio-event-loop>` with various system-specific
implementations;
* :ref:`transport <asyncio-transport>` and :ref:`protocol <asyncio-protocol>` abstractions
(similar to those in `Twisted <https://twistedmatrix.com/trac/>`_);
* concrete support for TCP, UDP, SSL, subprocess pipes, delayed calls, and
others (some may be system-dependent);
* a :class:`Future` class that mimics the one in the :mod:`concurrent.futures`
module, but adapted for use with the event loop;
* coroutines and tasks based on ``yield from`` (:PEP:`380`), to help write
concurrent code in a sequential fashion;
* cancellation support for :class:`Future`\s and coroutines;
* :ref:`synchronization primitives <asyncio-sync>` for use between coroutines in
a single thread, mimicking those in the :mod:`threading` module;
* an interface for passing work off to a threadpool, for times when
you absolutely, positively have to use a library that makes blocking
I/O calls.
Asynchronous programming is more complex than classical "sequential"
programming: see the :ref:`Develop with asyncio <asyncio-dev>` page which lists
common traps and explains how to avoid them. :ref:`Enable the debug mode
<asyncio-debug-mode>` during development to detect common issues.
Table of contents:
.. toctree::
:maxdepth: 3
asyncio-eventloop.rst
asyncio-eventloops.rst
asyncio-task.rst
asyncio-protocol.rst
asyncio-stream.rst
asyncio-subprocess.rst
asyncio-sync.rst
asyncio-queue.rst
asyncio-dev.rst
.. seealso::
The :mod:`asyncio` module was designed in :PEP:`3156`. For a
motivational primer on transports and protocols, see :PEP:`3153`.
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