Comment by eqvinox

14 hours ago

Hm, it doesn't seem to be dealing particularly well with imported packages that don't have type annotations. Seeing a bunch of "has no attribute" warnings. Some of the "substitute" annotations also seem to be wrong (e.g. asyncio in CPython has no annotations [in my installed version], but it's pulling some in from somewhere and they're not quite right…) It's also getting confused about lists and tuples in __slots__.

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eqvinox

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notatallshaw  14 hours ago

The standard library does not directly include type hints, they are stored in typeshed: https://github.com/python/typeshed

You can take a look yourself if you think some of them are wrong: https://github.com/python/typeshed/tree/main/stdlib/asyncio

The advantage is type hints can be fixed without needing to release a new version of Python. The disadvantage is there's a lot of code in the standard library that doesn't really consider how to represent it with type hints, and it can be really tricky and not always possible.

I'm surprised to see so many people moving to pyrefly, ty, and zuban so quickly. I was going to wait until some time in 2026 to see which has matured to the point I find useful, I guess some users really find existing solutions actually unworkable.

  • eqvinox  14 hours ago

    > You can take a look yourself if you think some of them are wrong: https://github.com/python/typeshed/tree/main/stdlib/asyncio

    Hmm. Presumably mypy and pyrefly use the same ones, but then I don't understand why pyrefly is complaining and mypy isn't:

      ERROR Argument `Future[list[BaseException | Any]]` is not assignable to parameter `future` with type `Awaitable[tuple[Any]]` in function `asyncio.events.AbstractEventLoop.run_until_complete` [bad-argument-type]
     --> xxx/xxx.py:513:33
      |
  513 |         loop.run_until_complete(tasks.gather(*x, return_exceptions=True))
      |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    The definition in typeshed is this:

      def run_until_complete(self, future: _AwaitableLike[_T]) -> _T: ...

    …where is it even puling "tuple[Any]" from…

    (tbh this is rather insignificant compared to the noise from external packages without type annotations, or with incomplete ones… pyrefly's inferences at the existence of attributes and their types are extremely conservative…)

    • notatallshaw  14 hours ago

      > Hmm. Presumably mypy and pyrefly use the same ones, but then I don't understand why pyrefly is complaining and mypy isn't:

      > …where is it even puling "tuple[Any]" from…

      Perhaps it's a bug in pyrefly, perhaps mypy or pyrefly is able to infer something about the types that the other isn't. I would strongly suggest checking their issues page, and if not seeing a report already report it yourself.

      While there is an ongoing push to more consistently document the typing spec: https://typing.python.org/. It does not actually cover all the things you can infer from type hints, and different type hint checkers have decided to take different design choices compared to mypy and will produce different errors even in the most ideal situation.

      This is one of the reasons why I am waiting for these libraries to mature a little more.

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