As discussed in < python/typeshed#3999 (comment) > the type of AbstractEventLoop.run_in_executor is defined at < https://github.com/python/cpython/blob/master/Lib/asyncio/events.py#L286 > as follows:

async def run_in_executor(self, executor, func, *args):
        raise NotImplementedError

However all concrete implementations of this method are actually not async methods but rather synchronous methods which return a Future object.

Logically this appears to make sense: at base run_in_executor is not a coroutine, since it doesn't create an object representing code which will be executed when the object is awaited, rather it returns an object representing code which is running asynchronously elsewhere (on another thread) and which can be awaited to wait for that other thread to complete its task. Which seems to be a perfect match to what a Future object is supposed to be.

As such it seems that the current definition of the method as a coroutine is possibly a mistake.

Alternatively if some feel that it is important to allow concrete implementations to implement it as a coroutine if they need to then perhaps it could be specified to be a method returning an Awaitable, since that would cover both options?

From looking at the commit history of AbstactEventLoop.run_in_executor(), it seems that it was previously be a non-coroutine method prior to the conversion from the @asyncio.coroutine decorator to async def (PR-4753). See https://github.com/python/cpython/blame/ede157331b4f9e550334900b3b4de1c8590688de/Lib/asyncio/events.py#L305.

The only context for the change I can find is the following conversation between Andrew and Yury: #4753 (comment). However, the example provided of connect_read_pipe() had already been a coroutine at the time for the BaseEventLoop implementation, which makes sense in that case. So, it's not clear to me as to why run_in_executor() was also converted to "async def" when its main implementation is not a coroutine. Furthermore, it's documented as an awaitable rather than a coroutine (https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.loop.run_in_executor).

@andrew do you have any additional context to provide that I'm potentially missing?

Is there any further movement on this?

I think it makes sense to remove the async from the definition in AbstractEventLoop.

If you want to help, you can submit a PR to do it.

#21852

New changeset 29f8429 by James Weaver in branch 'master':
bpo-40782: Change asyncio.AbstractEventLoop.run_in_executor to be a method not a coroutine (GH-21852)
29f8429

New changeset 1baa8b1 by Miss Islington (bot) in branch '3.8':
bpo-40782: Change asyncio.AbstractEventLoop.run_in_executor to be a method not a coroutine (GH-21852)
1baa8b1

New changeset d6bdf6d by Miss Islington (bot) in branch '3.9':
bpo-40782: Change asyncio.AbstractEventLoop.run_in_executor to be a method not a coroutine (GH-21852)
d6bdf6d