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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Should `asyncio.iscoroutinefunction` return some kind of `TypeGuard`?","articleBody":"I have the following use-case of a class that takes a regular function or a coroutine as an attribute, and then provides access to it through two properties. Basically the code looks like this:\r\n\r\n```python\r\n\"\"\"example.py\"\"\"\r\n\r\nfrom asyncio import iscoroutinefunction\r\nfrom typing import TypeVar, Generic, Callable, Awaitable, Any\r\n\r\nT = TypeVar('T')\r\n\r\nclass Response(Generic[T]):\r\n    ...\r\n\r\nclass Request(Generic[T]):\r\n    ...\r\n\r\nclass Foo:\r\n    def __init__(self, callback: Callable[[Request[T]], Response[T] | Awaitable[Response[T]]]):\r\n        self._callback = callback\r\n\r\n    @property\r\n    def func(self) -\u003e Callable[[Request[T]], Response[T]]:\r\n        if iscoroutinefunction(self._callback):\r\n            raise AttributeError()\r\n\r\n        return self._callback\r\n\r\n    @property\r\n    def coro(self) -\u003e Callable[[Request[T]], Awaitable[Response[T]]:\r\n        if not iscoroutinefunction(self._callback):\r\n            raise AttributeError()\r\n\r\n        return self._callback\r\n\r\nasync def bar(req: Request[T]) -\u003e Response[T]:\r\n    ...\r\n\r\nfoo = Foo(bar)\r\n\r\n```\r\n\r\nNow, I expected mypy to give no errors due to type narrowing from `iscoroutinefunction, but instead I get\r\n```\r\nexample.py:21: error: Incompatible return value type (got \"Callable[[Request[T]], Union[Response[T], Awaitable[Response[T]]]]\", expected \"Callable[[Request[T]], Response[T]]\")\r\nexample.py:28: error: Incompatible return value type (got \"Callable[[Request[T]], Union[Response[T], Awaitable[Response[T]]]]\", expected \"Callable[[Request[T]], Awaitable[Response[T]]]\")\r\n```\r\n\r\nAfter finding this, I started searching through the issues in both mypy and typeshed but couldn't find anything related to `iscoroutinefunction`. I then looked into typeshed and saw that the return type of `iscoroutinefunction` is just `bool`, and not a `TypeGuard`, despite the similar `iscoroutine` having one. This makes me think that `iscoroutinefunction` is annotated like that on purpose.\r\n\r\nSo my question is, should the return type of `asyncio.iscoroutinefunction` be a `TypeGuard` of some kind?\r\n\r\nI'm new to the more advanced features of Python typing, and my naive implementation would be something like\r\n```python\r\nfrom typing import TypeVar, TypeGuard\r\n\r\nT = TypeVar('T')\r\n\r\ndef iscoroutinefunction(func: T) -\u003e TypeGuard[T]: ...\r\n```\r\n\r\nIf you feel like this should be changed, I'd be happy to submit a PR once I know what the type should be.\r\n","author":{"url":"https://github.com/ajoino","@type":"Person","name":"ajoino"},"datePublished":"2022-06-01T18:46:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/8009/typeshed/issues/8009"}