[Async-sig] subclassing CancelledError

Hi, I want to ask how people feel about the following.

If you raise a subclass of CancelledError from within a task and then call task.result(), CancelledError is raised rather than the subclass.

Here is some code to illustrate:

class MyCancelledError(CancelledError): pass

async def raise_my_cancel(): raise MyCancelledError()

task = asyncio.ensure_future(raise_my_cancel()) try: await task except Exception: pass assert task.cancelled() # Raises CancelledError and not MyCancelledError. task.result()

Does this seem right to people? Is there a justification for this?

If it would help for the discussion, I could provide a use case.

Thanks a lot, --Chris