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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Incorrect pickling behavior in the c implemented classmethod descriptors","articleBody":"# Bug report\r\n\r\nHello there, this is my first bug report so apologies if there's something I miss.\r\n\r\nConsider the following code:\r\n```\r\nimport pickle\r\n\r\nclassmethod_descriptor = dict.__dict__[\"fromkeys\"]\r\nunpickled_classmethod_descriptor = pickle.loads(pickle.dumps(classmethod_descriptor, protocol=5))\r\n```\r\n\r\nWhile it passes without raising any errors, `classmethod_descriptor` differs from `unpickled_classmethod_descriptor`. Instead of the original descriptor, the pickling process yields the function itself:\r\n\r\n```\r\n\u003e\u003e\u003e classmethod_descriptor\r\n\u003cmethod 'fromkeys' of 'dict' objects\u003e\r\n\r\n\u003e\u003e\u003e unpickled_classmethod_descriptor\r\n\u003cfunction dict.fromkeys(iterable, value=None, /)\u003e\r\n```\r\n\r\nManually calling the descriptor's `__reduce_ex__` allows us to see the reason:\r\n```\r\n\u003e\u003e\u003e classmethod_descriptor.__reduce_ex__(5)\r\n(\u003cfunction getattr\u003e, (dict, 'fromkeys'))\r\n```\r\nThis behavior differs from python implemented classmethods:\r\n\r\n```\r\nimport pickle\r\n\r\nclass A:\r\n    @classmethod\r\n    def method(cls):\r\n        pass\r\n\r\nclassmethod_descriptor = A.__dict__[\"method\"]\r\n\r\n# Any of these lines will raise \"TypeError: cannot pickle 'classmethod' object\"\r\npickle.dumps(classmethod_descriptor, protocol=5)\r\nclassmethod_descriptor.__reduce_ex__(5)\r\n```\r\nSince it fails with normal classmethods, I would expect it to fail with their c counterparts as well so their behavior would match. \r\nEither that, or having both of them succeed during the pickling process, in which case, `__reduce_ex__` should return a valid result in both cases. \r\n\r\nThe bug occurs with other c implemented class methods as well:\r\n```\r\nimport pickle\r\n\r\nfrom datetime import datetime\r\n\r\nclassmethod_descriptor = datetime.__dict__[\"now\"]\r\n\r\n# Returns False\r\npickle.loads(pickle.dumps(classmethod_descriptor, 5)) == classmethod_descriptor\r\n\r\n# Returns True\r\npickle.loads(pickle.dumps(classmethod_descriptor, 5)) == datetime.now\r\n```\r\n\r\n# Your environment\r\nPython Versions:\r\nI've tested it with both 3.10.5 and 3.11.04b\r\nOS - Windows 10 Pro 64 bit\r\n\r\n\u003c!--\r\nYou can freely edit this text. Remove any lines you believe are unnecessary.\r\n--\u003e\r\n","author":{"url":"https://github.com/UltimateLobster","@type":"Person","name":"UltimateLobster"},"datePublished":"2022-07-24T09:40:36.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/95196/cpython/issues/95196"}