.. module:: asyncio
   :synopsis: Asynchronous I/O, event loop, coroutines and tasks.

.. 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);
• 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`.