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.

See also

A Conceptual Overview of asyncio

Explanation of the fundamentals of asyncio.

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.

Availability: not WASI.

This module does not work or is not available on WebAssembly. See WebAssembly platforms for more information.

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'

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

Raises an auditing event cpython.run_stdin with no arguments.

Changed in version 3.12.5: (also 3.11.10, 3.10.15, 3.9.20, and 3.8.20) Emits audit events.

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

Reference

High-level APIs

• Runners
• Coroutines and Tasks
• Streams
• Synchronization Primitives
• Subprocesses
• Queues
• Exceptions
• Call Graph Introspection

Low-level APIs

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

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/.