For long time I wanted to replace the use ofPyObject_IsInstance() withCancelledError in_asynciomodule.c. Even if the C code is correct and is closest to the corresponding Python code, it looked unnecessary complicated and bugprone. Also,PyErr_GivenExceptionMatches() is used inexcept implementation, so it may be more correct than an isinstance check. But I did not have tests for CancelledError subclasses which would show the difference.

Other issue.@gvanrossumnoticed thatasyncio.timeout() only checks for exact CancelledError, and not its subclasses.asyncio.TaskGroup() also only checks for exact CancelledError. It is suspicious, because all other code (except_convert_future_exc() infutures.py) treats CancelledError subclasses in the same way as CancelledError.asyncio.timeout() andasyncio.TaskGroup() were added recently, so perhaps it is error in their implementation. On other hand, I do not know any use case for CancelledError subclasses.

Linked PRs

• gh-113848: Use PyErr_GivenExceptionMatches() for check for CancelledError #113849
• gh-113848: Handle CancelledError subclasses in asyncio TaskGroup() and timeout() #113850