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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`__annotate__` does not get called if `__annotations__` exist","articleBody":"This code:\r\n\r\n```python\r\nclass A:\r\n    x: int\r\n    y: str\r\n\r\n    def __annotate__(format):\r\n        return {'a': bool}\r\n\r\nimport annotationlib\r\nprint(A.__annotations__)\r\nprint(annotationlib.get_annotations(A, format=annotationlib.Format.VALUE))\r\nprint(annotationlib.get_annotations(A, format=annotationlib.Format.FORWARDREF))\r\nprint(annotationlib.get_annotations(A, format=annotationlib.Format.SOURCE))\r\n```\r\n\r\nProduces:\r\n\r\n```\r\n{'x': \u003cclass 'int'\u003e, 'y': \u003cclass 'str'\u003e}\r\n{'x': \u003cclass 'int'\u003e, 'y': \u003cclass 'str'\u003e}\r\n{'x': \u003cclass 'int'\u003e, 'y': \u003cclass 'str'\u003e}\r\n{'x': 'int', 'y': 'str'}\r\n```\r\n\r\nPEP 649 specifies this as: https://peps.python.org/pep-0649/#annotate-and-annotations\r\n\r\n```\r\nWhen o.__annotations__ is evaluated, and the internal storage for o.__annotations__ is unset, and o.__annotate__ is set to a callable, the getter for o.__annotations__ calls o.__annotate__(1), then caches the result in its internal storage and returns the result.\r\n\r\nTo explicitly clarify one question that has come up multiple times: this o.__annotations__ cache is the only caching mechanism defined in this PEP. There are no other caching mechanisms defined in this PEP. The __annotate__ functions generated by the Python compiler explicitly don’t cache any of the values they compute.\r\n```\r\n\r\nComment them out:\r\n\r\n```python\r\nclass A:\r\n    # x: int\r\n    # y: str\r\n\r\n    def __annotate__(format):\r\n        return {'a': bool}\r\n\r\nimport annotationlib\r\nprint(A.__annotations__)\r\nprint(annotationlib.get_annotations(A, format=annotationlib.Format.VALUE))\r\nprint(annotationlib.get_annotations(A, format=annotationlib.Format.FORWARDREF))\r\nprint(annotationlib.get_annotations(A, format=annotationlib.Format.SOURCE))\r\n```\r\n\r\nProduces:\r\n\r\n```python\r\n{'a': \u003cclass 'bool'\u003e}\r\n{'a': \u003cclass 'bool'\u003e}\r\n{'a': \u003cclass 'bool'\u003e}\r\n{'a': \u003cclass 'bool'\u003e}\r\n```\r\n\r\nLet's discuss this.","author":{"url":"https://github.com/sobolevn","@type":"Person","name":"sobolevn"},"datePublished":"2024-07-25T14:40:12.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":12},"url":"https://github.com/122285/cpython/issues/122285"}