asyncio CancelledError and KeyboardInterrupt

Question

I\'m trying 2 ways to stop an infinite loop from running:

• supervisor_1: task is canceled programatically
• supervisor_2

Answer 1

task.cancel() itself doesn't finish the task: it just says to task that CancelledError should be raised inside it and returns immediately. You should call it and await while task would be actually cancelled (while it'll raise CancelledError).

You also shouldn't suppress CancelledError inside task.

Read this answer where I tried to show different ways of working with tasks. For example to cancel some task and await it cancelled you can do:

from contextlib import suppress


task = ...  # remember, task doesn't suppress CancelledError itself

task.cancel()  # returns immediately, we should await task raised CancelledError.

with suppress(asyncio.CancelledError):
    await task  # or loop.run_until_complete(task) if it happens after event loop stopped

# Now when we awaited for CancelledError and handled it, 
# task is finally over and we can close event loop without warning.