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

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

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;

For introspection, asyncio provides APIs and tools for:

  • inspecting the :ref:`async call graph <asyncio-graph>` of tasks and futures;
  • inspecting tasks in another running Python process with :ref:`command-line tools <asyncio-introspection-tools>`;

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.

asyncio REPL

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

$ 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.

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


.. toctree::
   :caption: Introspection APIs
   :maxdepth: 1

   asyncio-graph.rst
   asyncio-tools.rst


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

   asyncio-eventloop.rst
   asyncio-future.rst
   asyncio-protocol.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
   asyncio-threading.rst

Note

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