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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Allow `types.GeneratorType` to be used instead of `collections.abc.Generator` as the return type of generator functions","articleBody":"**Feature**\n\nCurrently, mypy only allows [`collections.abc.Generator`](https://docs.python.org/3/library/collections.abc.html#collections.abc.Generator) and its supertypes as the return type of generator functions, and as a result, it cannot infer the correct return type for awaitable objects that define the [`__await__()`](https://docs.python.org/3/reference/datamodel.html#object.__await__) method via [`types.GeneratorType`](https://docs.python.org/3/library/types.html#types.GeneratorType):\n\n```python\nimport asyncio\n\nfrom collections.abc import Generator\nfrom types import GeneratorType\nfrom typing import Never, reveal_type\n\n\nclass A:\n    def __await__(self) -\u003e GeneratorType[Never, Never, bool]:\n        return True\n        yield  # generator definition\n\n\nclass B:\n    def __await__(self) -\u003e Generator[Never, Never, bool]:\n        return True\n        yield  # generator definition\n\n\nasync def main() -\u003e None:\n    reveal_type(await A())  # revealed type is \"Any\"\n    reveal_type(await B())  # revealed type is \"builtins.bool\"\n\n    reveal_type(A().__await__().gi_running)  # revealed type is \"builtins.bool\"\n    reveal_type(B().__await__().gi_running)  # has no attribute \"gi_running\"\n\n\nif __name__ == \"__main__\":\n    asyncio.run(main())\n```\n\n```\nexample.py:9: error: The return type of a generator function should be \"Generator\" or one of its supertypes  [misc]\nexample.py:21: note: Revealed type is \"Any\"\nexample.py:22: note: Revealed type is \"builtins.bool\"\nexample.py:24: note: Revealed type is \"builtins.bool\"\nexample.py:25: error: \"Generator[Never, Never, bool]\" has no attribute \"gi_running\"  [attr-defined]\nexample.py:25: note: Revealed type is \"Any\"\nFound 2 errors in 1 file (checked 1 source file)\n```\n\nI propose allowing the use of [`types.GeneratorType`](https://docs.python.org/3/library/types.html#types.GeneratorType) with subsequent inference of the correct return type.\n\n**Pitch**\n\nFirst, [pyright](https://github.com/microsoft/pyright) already has the expected behavior:\n\n```\n/home/user/workspace/example.py\n  /home/user/workspace/example.py:21:17 - information: Type of \"await A()\" is \"bool\"\n  /home/user/workspace/example.py:22:17 - information: Type of \"await B()\" is \"bool\"\n  /home/user/workspace/example.py:24:17 - information: Type of \"A().__await__().gi_running\" is \"bool\"\n  /home/user/workspace/example.py:25:17 - information: Type of \"B().__await__().gi_running\" is \"Unknown\"\n  /home/user/workspace/example.py:25:33 - error: Cannot access attribute \"gi_running\" for class \"Generator[Never, Never, bool]\"\n    Attribute \"gi_running\" is unknown (reportAttributeAccessIssue)\n1 error, 0 warnings, 4 informations\n```\n\nSecond, this relates to the eternally controversial python/typing#1480. In python/typeshed#10816, false properties related to native objects were removed in favor of the [`types`](https://docs.python.org/3/library/types.html) module. You could say that we can use [`isinstance`](https://docs.python.org/3/library/functions.html#isinstance)/[`inspect.isgenerator`](https://docs.python.org/3/library/inspect.html#inspect.isgenerator) to narrow [`collections.abc.Generator`](https://docs.python.org/3/library/collections.abc.html#collections.abc.Generator) down to [`types.GeneratorType`](https://docs.python.org/3/library/types.html#types.GeneratorType), but... it is not that simple:\n\n```python\n    x = B().__await__()\n    reveal_type(x)  # typing.Generator[Never, Never, builtins.bool]\n\n    if isgenerator(x):\n        reveal_type(x)  # types.GeneratorType[Any, Any, Any]\n\n    if isinstance(x, GeneratorType):\n        reveal_type(x)  # types.GeneratorType[Any, Any, Any]\n```\n\nI think that allowing the use of [`types.GeneratorType`](https://docs.python.org/3/library/types.html#types.GeneratorType) would make it easier to inspect native generator objects. Especially since [`collections.abc.Generator`](https://docs.python.org/3/library/collections.abc.html#collections.abc.Generator) can also be used to define custom generator types.\n\nRelated: #18635.","author":{"url":"https://github.com/x42005e1f","@type":"Person","name":"x42005e1f"},"datePublished":"2026-01-04T18:01:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/20522/mypy/issues/20522"}