Sounds like an implementation issue. The Future class has a boolean flag indicating whether it's been cancelled, and everything then raises CancelledError when that flag is set. I suppose we could replace that flag with an instance of CancelledError, and when we *catch* CancelledError we set it to that. But it seems messy and I'm not sure that you should attempt this. IMO you should define an exception that does *not* derive from CancelledError and raise that -- it will properly be transmitted. What's your reason for not doing that? IOW why are you trying to pump more than a bit through the narrow "cancelled" channel?
On Sun, Dec 3, 2017 at 2:11 AM, Andrew Svetlov email@example.com wrote:
IIRC at very early stages Guido van Rossum decided to *freeze* `CancelledError`: user code should not derive from the exception. Like you never derive from StopIteration.
On Sun, Dec 3, 2017 at 8:00 AM Chris Jerdonek firstname.lastname@example.org wrote:
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 _______________________________________________ Async-sig mailing list Asyncemail@example.com https://mail.python.org/mailman/listinfo/async-sig Code of Conduct: https://www.python.org/psf/codeofconduct/
-- Thanks, Andrew Svetlov
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