René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"All exceptions are swallowed when looking up `__set_name__` on an object in a class namespace during construction of that class","articleBody":"# Bug report\n\n### Bug description:\n\nDuring construction of a class `Foo`, all objects in the class dictionary are checked to see if they have a `__set_name__` attribute. If an object in the dictionary does have a `__set_name__` attribute, it is called as part of the construction of `Foo`:\n\n```pycon\n\u003e\u003e\u003e class Vanilla:\n...     def __set_name__(self, owner, name):\n...         print('set_name called')\n...\n\u003e\u003e\u003e class Foo:\n...     attr = Vanilla()\n...\nset_name called\n```\n\nBut what if an object in a class namespace is an instance of class that has a metaclass that raises a non-`AttributeError` exception if `__set_name__` is looked up on the class object? In this case, the exception is silently ignored when `__set_name__` is looked up:\n\n```pycon\n\u003e\u003e\u003e class Meta(type):\n...     def __getattribute__(self, attr):\n...         if attr == \"__set_name__\":\n...             raise SystemExit('NO')\n...         return object.__getattribute__(self, attr)\n...\n\u003e\u003e\u003e class Problematic(metaclass=Meta): pass\n...\n\u003e\u003e\u003e try:\n...     Problematic.__set_name__\n... except SystemExit:\n...     print('exception was raised')\n...\nexception was raised\n\u003e\u003e\u003e class Bar:\n...     attr = Problematic()\n...\n\u003e\u003e\u003e\n```\n\n`__set_name__`, like all dunders, is looked up on the `Problematic` class object itself, rather than the instance of `Problematic` found in the class dictionary of `Foo`, so `SystemExit` should be raised during the creation of the `Bar` class when the interpreter tries to determine whether or not the `Problematic` class has a `__set_name__` attribute. Instead, however, the `SystemExit` is silently swallowed.\n\nI think the issue lies in this section of code here:\n\nhttps://github.com/python/cpython/blob/d44ee42cd7c9a40e1d7096b95476fe47156f571f/Objects/typeobject.c#L9989-L9992\n\nI'm interested in working on this.\n\n### CPython versions tested on:\n\n3.8, CPython main branch\n\n### Operating systems tested on:\n\nWindows","author":{"url":"https://github.com/AlexWaygood","@type":"Person","name":"AlexWaygood"},"datePublished":"2023-11-27T13:09:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/112453/cpython/issues/112453"}