asyncio — 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:

• run Python coroutines concurrently and have full control over their execution;

• perform network IO and IPC;

• control subprocesses;

• distribute tasks via queues;

• synchronize concurrent code;

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

• create and manage event loops, which provide asynchronous APIs for networking, running subprocesses, handling OS signals, etc;

• implement efficient protocols using transports;

• bridge callback-based libraries and code with async/await syntax.

asyncio REPL

You can experiment with an asyncio concurrent context in the 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'

Raises an auditing event cpython.run_stdin with no arguments.

Changed in version 3.9.20: (also 3.8.20) Emits audit events.

Reference

High-level APIs

• Coroutines and Tasks
• Streams
• Synchronization Primitives
• Subprocesses
• Queues
• Exceptions

Low-level APIs

• Event Loop
• Futures
• Transports and Protocols
• Policies
• Platform Support

Guides and Tutorials

• High-level API Index
• Low-level API Index
• Developing with asyncio

Note

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