: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.
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.
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'.. 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 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/`.