:mod:!asyncio --- Asynchronous I/O

.. module:: asyncio :synopsis: Asynchronous I/O.

.. sidebar:: Hello World!

::

   import asyncio

   async def main():
       print('Hello ...')
       await asyncio.sleep(1)
       print('... World!')

   asyncio.run(main())

asyncio is a library to write concurrent code using the async/await syntax.

asyncio is used as a foundation for multiple Python asynchronous frameworks that provide high-performance network and web-servers, database connection libraries, distributed task queues, etc.

asyncio is often a perfect fit for IO-bound and high-level structured network code.

.. seealso::

:ref:a-conceptual-overview-of-asyncio Explanation of the fundamentals of asyncio.

asyncio provides a set of high-level APIs to:

• :ref:run Python coroutines <coroutine> concurrently and have full control over their execution;

• perform :ref:network IO and IPC <asyncio-streams>;

• control :ref:subprocesses <asyncio-subprocess>;

• distribute tasks via :ref:queues <asyncio-queues>;

• :ref:synchronize <asyncio-sync> concurrent code;

Additionally, there are low-level APIs for library and framework developers to:

• create and manage :ref:event loops <asyncio-event-loop>, which provide asynchronous APIs for :ref:networking <loop_create_server>, running :ref:subprocesses <loop_subprocess_exec>, handling :ref:OS signals <loop_add_signal_handler>, etc;

• implement efficient protocols using :ref:transports <asyncio-transports-protocols>;

• :ref:bridge <asyncio-futures> callback-based libraries and code with async/await syntax.

.. include:: ../includes/wasm-notavail.rst

.. _asyncio-cli:

.. rubric:: asyncio REPL

You can experiment with an asyncio concurrent context in the :term:REPL:

.. code-block:: pycon

$ python -m asyncio asyncio REPL ... Use "await" directly instead of "asyncio.run()". Type "help", "copyright", "credits" or "license" for more information.

import asyncio await asyncio.sleep(10, result='hello') 'hello'

This REPL provides limited compatibility with :envvar:PYTHON_BASIC_REPL. It is recommended that the default REPL is used for full functionality and the latest features.

.. audit-event:: cpython.run_stdin "" ""

.. versionchanged:: 3.12.5 (also 3.11.10, 3.10.15, 3.9.20, and 3.8.20) Emits audit events.

.. versionchanged:: 3.13 Uses PyREPL if possible, in which case :envvar:PYTHONSTARTUP is also executed. Emits audit events.

.. We use the "rubric" directive here to avoid creating the "Reference" subsection in the TOC.

.. rubric:: Reference

.. toctree:: :caption: High-level APIs :maxdepth: 1

asyncio-runner.rst asyncio-task.rst asyncio-stream.rst asyncio-sync.rst asyncio-subprocess.rst asyncio-queue.rst asyncio-exceptions.rst asyncio-graph.rst

.. toctree:: :caption: Low-level APIs :maxdepth: 1

asyncio-eventloop.rst asyncio-future.rst asyncio-protocol.rst asyncio-policy.rst asyncio-platforms.rst asyncio-extending.rst

.. toctree:: :caption: Guides and Tutorials :maxdepth: 1

asyncio-api-index.rst asyncio-llapi-index.rst asyncio-dev.rst

.. note:: The source code for asyncio can be found in :source:Lib/asyncio/.