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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Occasional incorrect chaining of CancelledError when calling 'cancel' on result of 'asyncio.gather'","articleBody":"```python\r\nimport asyncio\r\n\r\nasync def f1():\r\n    await asyncio.sleep(1)\r\n\r\nasync def f2():\r\n    return 42\r\n\r\nasync def main():\r\n    # case 1\r\n    gfut = asyncio.gather(f1(), f2(), return_exceptions=True)\r\n    # case 2\r\n    #gfut = asyncio.gather(f2(), f1(), return_exceptions=True)\r\n    await asyncio.sleep(0.1)\r\n    gfut.cancel(\"my message\")\r\n    await gfut\r\n\r\nasyncio.run(main())\r\n\r\n# case 1\r\n\r\n#Traceback (most recent call last):\r\n#  File \"/Users/vladima/Sources/gather.py\", line 14, in main\r\n#    print(await gfut)\r\n#asyncio.exceptions.CancelledError\r\n#\r\n#During handling of the above exception, another exception occurred:\r\n#\r\n#Traceback (most recent call last):\r\n#  File \"/Users/vladima/Sources/gather.py\", line 16, in \u003cmodule\u003e\r\n#    asyncio.run(main())\r\n#  File \"/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/runners.py\", line 44, in run\r\n#    return loop.run_until_complete(main)\r\n#  File \"/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/base_events.py\", line 646, in run_until_complete\r\n#    return future.result()\r\n#asyncio.exceptions.CancelledError\r\n\r\n# case 2\r\n#Traceback (most recent call last):\r\n#  File \"/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/tasks.py\", line 605, in sleep\r\n#    return await future\r\n#asyncio.exceptions.CancelledError: my message\r\n\r\n#During handling of the above exception, another exception occurred:\r\n\r\n#Traceback (most recent call last):\r\n#  File \"/Users/vladima/Sources/gather.py\", line 14, in main\r\n#    print(await gfut)\r\n#asyncio.exceptions.CancelledError\r\n#\r\n#During handling of the above exception, another exception occurred:\r\n#\r\n#Traceback (most recent call last):\r\n#  File \"/Users/vladima/Sources/gather.py\", line 16, in \u003cmodule\u003e\r\n#    asyncio.run(main())\r\n#  File \"/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/runners.py\", line 44, in run\r\n#    return loop.run_until_complete(main)\r\n#  File \"/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/base_events.py\", line 646, in run_until_complete\r\n#    return future.result()\r\n#asyncio.exceptions.CancelledError\r\n```\r\n\r\nCurrently traceback and description parts of `CancelledError` depend upon the order of arguments that were passed into `asyncio.gather`. The reason I believe is [this](https://github.com/python/cpython/blob/main/Lib/asyncio/tasks.py#L812): here `fut` would be bound to the last item in `children` which might or might not correspond to the cancelled task and instead it should probably be one of tasks that were actually cancelled  (which is still not ideal since there might be many of them but I guess with `gather` it is as good as it can be).\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-133243\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/vladima","@type":"Person","name":"vladima"},"datePublished":"2022-10-05T14:53:55.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/97907/cpython/issues/97907"}