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async_generator

Async generators and context managers for Python 3.5+

    1.10

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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 async_generator, yield_

   @async_generator
   async def load_json_lines(stream_reader):
       async for line in stream_reader:
           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 async_generator, yield_, asynccontextmanager

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


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