The async_generator library

Python 3.6 added async generators <https://www.python.org/dev/peps/pep-0525/>. (What's an async generator? Check out my 5-minute lightning talk demo from PyCon 2016 <https://youtu.be/PulzIT8KYLk?t=24m30s>.) Python 3.7 adds some more tools to make them usable, like contextlib.asynccontextmanager.

This library gives you all that back to Python 3.5.

For example, this code only works in Python 3.6+:

.. code-block:: python3

async def load_json_lines(stream_reader): async for line in stream_reader: yield json.loads(line)

But this code does the same thing, and works on Python 3.5+:

.. code-block:: python3

from async_generator import asyncgenerator, yield

@async_generator async def load_json_lines(stream_reader): async for line in streamreader: await yield(json.loads(line))

Or in Python 3.7, you can write:

.. code-block:: python3

from contextlib import asynccontextmanager

@asynccontextmanager async def background_server(): async with trio.open_nursery() as nursery: value = await nursery.start(my_server) try: yield value finally:

Kill the server when the scope exits

           nursery.cancel_scope.cancel()

This is the same, but back to 3.5:

.. code-block:: python3

from async_generator import asyncgenerator, yield, asynccontextmanager

@asynccontextmanager @async_generator async def background_server(): async with trio.open_nursery() as nursery: value = await nursery.start(myserver) try: await yield(value) finally:

Kill the server when the scope exits

           nursery.cancel_scope.cancel()

(And if you're on 3.6, you can use @asynccontextmanager with native generators.)

Let's do this

Install: python3 -m pip install -U async_generator (or on Windows, maybe py -3 -m pip install -U async_generator
Manual: https://async-generator.readthedocs.io/
Bug tracker and source code: https://github.com/python-trio/async_generator
Real-time chat: https://gitter.im/python-trio/general
License: MIT or Apache 2, your choice
Contributor guide: https://trio.readthedocs.io/en/latest/contributing.html
Code of conduct: Contributors are requested to follow our code of conduct <https://trio.readthedocs.io/en/latest/code-of-conduct.html>__ in all project spaces.

How come some of those links talk about "trio"?

Trio <https://trio.readthedocs.io>__ is a new async concurrency library for Python that's obsessed with usability and correctness – we want to make it easy to get things right. The async_generator library is maintained by the Trio project as part of that mission, and because Trio uses async_generator internally.

You can use async_generator with any async library. It works great with asyncio, or Twisted, or whatever you like. (But we think Trio is pretty sweet.)

python-trio / async_generator

readme

The async_generator library

Kill the server when the scope exits

Kill the server when the scope exits

Let's do this

How come some of those links talk about "trio"?