# `asyncio` — Asynchronous I/O

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.

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'

Availability: not Emscripten, not WASI.

This module does not work or is not available on WebAssembly platforms `wasm32-emscripten` and `wasm32-wasi`. See WebAssembly platforms for more information.

Reference

High-level APIs

- Runners
- Coroutines and Tasks
- Streams
- Synchronization Primitives
- Subprocesses
- Queues
- Exceptions

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/.