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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Inconsistency in handling None handlers in the Python and C implementations of pickle","articleBody":"In the Python implementation of `pickle` setting some handlers to None causes a fallback to other methods.\r\n* Setting `Pickler.reducer_override` to None has the same effect as not setting this attribute -- falling back to other methods.\r\n* Setting the `dispatch_table` to None leads to falling back to `__reduce_ex__`.\r\n* Setting the `__reduce_ex__` attribute to None leads to falling back to `__reduce__`.\r\n* Setting the `__setstate__` attribute to None leads to falling back to the default implementation of `__setstate__` (setting `__dict__` and slots).\r\n\r\nIn the C implementation all this leads to `TypeError: 'NoneType' object is not callable`.\r\n\r\nThe `copy` module follows the Python implementation of `pickle`, except that it fails for any false value of `__reduce__`, not just None.\r\n\r\nIn most other code setting a dunder method to None leads to a TypeError (either raise explicitly or just generic \"'NoneType' object is not callable\").\r\n\r\nWe should decide what behavior should be in the `pickle` and `copy` module. On one hand, the Python implementation was primary. On other hand, it was inconsistent between the `pickle` and `copy` modules and was already changed in the past, the C implementation of `pickle` is now used by most users, and it is more consistent with other code.\r\n\r\nSee also:\r\nhttps://mail.python.org/archives/list/python-dev@python.org/thread/YGAK34DRWJFSIV2VZ4NC2J24XO37GCMM/\r\nhttps://docs.python.org/3.10/reference/datamodel.html#id2\r\nhttps://github.com/python/cpython/issues/70146\r\nhttps://github.com/python/cpython/issues/55781\r\nhttps://github.com/python/cpython/issues/60755\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-103035\n* gh-109498\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/serhiy-storchaka","@type":"Person","name":"serhiy-storchaka"},"datePublished":"2022-06-09T04:29:12.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/93627/cpython/issues/93627"}