18.5.asyncio — Asynchronous I/O, event loop, coroutines and tasks¶

Source code:Lib/asyncio/

This module provides infrastructure for writing single-threaded concurrentcode using coroutines, multiplexing I/O access over sockets and otherresources, running network clients and servers, and other related primitives.Here is a more detailed list of the package contents:

• a pluggableevent loop with various system-specificimplementations;
• transport andprotocol abstractions(similar to those inTwisted);
• concrete support for TCP, UDP, SSL, subprocess pipes, delayed calls, andothers (some may be system-dependent);
• aFuture class that mimics the one in theconcurrent.futuresmodule, but adapted for use with the event loop;
• coroutines and tasks based onyieldfrom (PEP 380), to help writeconcurrent code in a sequential fashion;
• cancellation support forFutures and coroutines;
• synchronization primitives for use between coroutines ina single thread, mimicking those in thethreading module;
• an interface for passing work off to a threadpool, for times whenyou absolutely, positively have to use a library that makes blockingI/O calls.

Asynchronous programming is more complex than classical “sequential”programming: see theDevelop with asyncio page which listscommon traps and explains how to avoid them.Enable the debug mode during development to detect common issues.

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