:mod:`asyncio` -- 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.
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: