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

• a pluggable event loop with various system-specific implementations;
• transport and protocol abstractions (similar to those in Twisted);
• concrete support for TCP, UDP, SSL, subprocess pipes, delayed calls, and others (some may be system-dependent);
• a Future class that mimics the one in the concurrent.futures module, but adapted for use with the event loop;
• coroutines and tasks based on yield from (PEP 380), to help write concurrent code in a sequential fashion;
• cancellation support for Futures and coroutines;
• synchronization primitives for use between coroutines in a single thread, mimicking those in the threading module;
• an interface for passing work off to a threadpool, for times when you absolutely, positively have to use a library that makes blocking I/O calls.

Note: The implementation of asyncio was previously called "Tulip".

Installation

To install asyncio, type:

pip install asyncio

asyncio requires Python 3.3 or later! The asyncio module is part of the Python standard library since Python 3.4.

asyncio is a free software distributed under the Apache license version 2.0.

Websites

• asyncio project at GitHub: source code, bug tracker
• asyncio documentation
• Mailing list: python-tulip Google Group
• IRC: join the #asyncio channel on the Freenode network

Development

The actual code lives in the 'asyncio' subdirectory. Tests are in the 'tests' subdirectory.

To run tests, run:

tox

Or use the Makefile:

make test

To run coverage (coverage package is required):

make coverage

On Windows, things are a little more complicated. Assume P is your Python binary (for example C:\Python33\python.exe).

You must first build the _overlapped.pyd extension and have it placed in the asyncio directory, as follows:

C:\> P setup.py build_ext --inplace

If this complains about vcvars.bat, you probably don't have the required version of Visual Studio installed. Compiling extensions for Python 3.3 requires Microsoft Visual C++ 2010 (MSVC 10.0) of any edition; you can download Visual Studio Express 2010 for free from http://www.visualstudio.com/downloads (scroll down to Visual C++ 2010 Express).

Once you have built the _overlapped.pyd extension successfully you can run the tests as follows:

C:\> P runtests.py

And coverage as follows:

C:\> P runtests.py --coverage