14.3. Async Awaitable

  • Since Python 3.5 PEP 492 -- Coroutines with async and await syntax

  • Object is an awaitable if it can be used in an await expression

  • Awaitable objects: Coroutines, Tasks, Futures

  • __await__ and await keyword

aw
awaitable

Object is an awaitable if it can be used in an await expression

aws

Awaitables

coroutine

Coroutine - a function which can run concurrently.

tasks

Runs thing in the "background". Can be awaited and cancelled.

future

An awaitable object generally implements an __await__() method. Coroutine objects returned from async def functions are awaitable. Note The generator iterator objects returned from generators decorated with types.coroutine() or asyncio.coroutine() are also awaitable, but they do not implement __await__().

object.__await__(self) Must return an iterator. Should be used to implement awaitable objects. For instance, asyncio.Future implements this method to be compatible with the await expression. [1]

../../_images/about-awaitables.png
../../_images/about-model-awaitables.png
../../_images/about-asyncio-sync-vs-async.png
../../_images/about-coroutine.png
../../_images/about-gather-awaitables.png 
>>> import asyncio
>>>
>>> async def say_hello():
...     return 'hello'

Awaitable:

>>> say_hello()

Awaitables:

>>> asyncio.gather(say_hello(), say_hello(), say_hello())  

>>> todo = [say_hello(), say_hello(), say_hello()]
>>> asyncio.gather(*todo)

14.3.1. Awaitables

There are three main types of awaitable objects:

  • Coroutines,

  • Tasks,

  • Futures.

Coroutines are a low level concept and doesn't know about asyncio concepts such as EventLoop and Cancellations.

Tasks wraps around a coroutine object and allows for handling exceptions, gathering results etc.

14.3.2. Objects

Features of Python:

>>> from collections.abc import Awaitable
>>> from collections.abc import Coroutine

Features of AsyncIO library:

>>> from asyncio import Future
>>> from asyncio import Task

14.3.3. Typing

>>> from collections.abc import Awaitable
>>> from collections.abc import Coroutine
>>> from collections.abc import AsyncIterable
>>> from collections.abc import AsyncIterator
>>> from collections.abc import AsyncGenerator

14.3.4. References