asyncio

Asyncio is a Python library that provides infrastructure for writing asynchronous I/O-bound programs using coroutines, an event loop, and tasks. It enables cooperative multitasking on a single thread by executing non-blocking I/O and other awaitable operations while yielding control to the event loop.

At the core is the event loop, which schedules and runs coroutines, futures, and callbacks. Coroutines are defined with async def and suspended at await expressions. Tasks wrap coroutines so they can be scheduled, canceled, and awaited. The library also offers high-level abstractions for streams and protocols and a mechanism to run blocking code in a thread or process pool via executors.

Key concepts include Futures, Awaitables, and Tasks; a Future represents a result that will be produced later. Awaiting a Future or Task suspends the coroutine until completion. Common helpers include asyncio.sleep, asyncio.gather, asyncio.wait, and queues to coordinate producers and consumers.

Usage typically involves defining async functions and launching them with asyncio.run to obtain a result. Multiple coroutines can be started with asyncio.create_task or asyncio.gather. To integrate with blocking code, run_in_executor can offload work to a thread or process pool.

Asyncio is part of the Python standard library since Python 3.4; async/await syntax was added in Python 3.5. It is widely used for network clients and servers, and in web frameworks such as aiohttp. It is most effective for I/O-bound workloads; CPU-bound tasks require separate threads, processes, or native extensions, and debugging asyncio programs can be challenging on some platforms.