When calling asyncio.ensure_future() on a coroutine, and if the loop is closed, ensure_future() will raise a RuntimeError.

However, it still creates a Task, which will generate a RuntimeWarning that we can’t fix since there is no way to cancel the Task.

Here is the code to reproduce the bug:

import asyncio

l = asyncio.get_event_loop()
l.close()

async def foo():
    pass

try:
# Since the exception raises here, fut is never set
# so we can't call fut.cancel()
fut = asyncio.ensure_future(foo())
except RuntimeError:
pass

# stderr:
# aio.py:12: RuntimeWarning: coroutine 'foo' was never awaited
# pass

Sounds like an easy fix. Could you submit a patch?

Reproduced on 3.11.

So I just realized that the OP's description is slightly misleading. (Their code is spot on though!)

The code does not create an unwaited-for *task*, assuming that "task" refers to the asyncio.Task class.

What is created is a *coroutine* object that's never awaited (as the quoted RuntimeWarning message says: "coroutine 'foo' was never awaited").

So the thing that needs to be closed in the bowels of _ensure_future() is indeed the argument (coro_or_future), in case it is a coroutine object.

New changeset 24cc641 by Kumar Aditya in branch 'main':
bpo-26552: Fixed case where failing asyncio.ensure_future did not close the coroutine (bpo-30288)
24cc641

Thanks Kumar for the fix!

New changeset a5451c9 by Kumar Aditya in branch '3.10':
bpo-26552: Fixed case where failing asyncio.ensure_future did not close the coroutine (bpo-30288) (bpo-31003)
a5451c9