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bpo-31033: Make traceback for cancelled asyncio tasks more useful #19951
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This moves (and renames) exc_state_clear() in genobject.c to _PyErr_ClearExcState() in pycore_pyerrors.h.
This simplifies calling _PyErr_ChainExceptions() when we want to set a _PyErr_StackItem as the exception context.
When an asyncio.Task is cancelled, the exception traceback now starts with where the task was first interrupted. Previously, the traceback only had "depth one."
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@1st1 Here's a new version of the PR after rebasing with PR #19979 and ensuring that the cancelled message isn't duplicated multiple times in the traceback. I'll show you what the output looks like in a comment after this. I wasn't able to get the tests passing using a weakref or setting Lines 360 to 363 in aa92a7c
Similarly, setting self._cancelled_exc to None wasn't working in certain tests for different reasons.
Can this be an optimization that's considered later? |
Here's an example to show you what the output look like. For this code: import asyncio, sys
async def nested():
fut = asyncio.sleep(1)
await fut # AWAIT #1
async def run():
task = asyncio.create_task(nested())
await asyncio.sleep(0)
task.cancel('POSSIBLY LONG CANCEL MESSAGE')
await task # AWAIT #2
loop = asyncio.new_event_loop()
try:
loop.run_until_complete(run())
finally:
loop.close() Here is before the PR:
And here is after the PR:
|
Okay, I was able to get it working with setting |
@1st1 Is there any way this can be merged by tomorrow? I addressed your first review comment (setting |
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Chris, this looks good and the usability improvement is huge. I've left a nit comment, feel free to address it in this PR or later, up to you. Thanks!
@ambv I think this needs to be included in 3.9. I'm going to merge it myself tomorrow morning if Chris doesn't. Or you can merge it as is! |
_PyErr_ChainStackItem was just added in pythonGH-19951 (for bpo-31033).
…H-19951) When an asyncio.Task is cancelled, the exception traceback now starts with where the task was first interrupted. Previously, the traceback only had "depth one."
_PyErr_ChainStackItem was just added in pythonGH-19951 (for bpo-31033).
When an asyncio.Task is cancelled, the exception traceback now starts with where the task was first interrupted.
Previously, the traceback only had "depth one," which wasn't too useful.
https://bugs.python.org/issue31033