python - 覆盖父类(super class)型的协程时如何使用 mypy？

Question

有一个类扩展了另一个类并覆盖了一个返回迭代器的协程:

class Repository:
     async def run(self, query: Query) -> AsyncIterator[int]:
...

class MyRepository(Repository):
     async def run(self, query: Query) -> AsyncIterator[int]:
...

运行 mypy 返回此错误:

error: Return type "AsyncIterator[int]" of "run" incompatible with return type "Coroutine[Any, Any, AsyncIterator[int]]" in supertype "Repository"

Coroutines are typed like normal functions ，所以我不确定正确的方法是什么。

使用 ABC 类无法解决问题:

class Repository(metaclass=ABCMeta):
    @abstractmethod
    async def run(self, query: Query) -> AsyncIterator[int]:

Answer 1

感谢 this issue 找到它:

I think you shouldn't make the protocol function async def, but just def. Conceptually, an async generator is a callable that returns an AsyncIterator (or more precisely, an AsyncGenerator). But an async def function without a yield returns an Awaitable of whatever its declared return type is, so that's how mypy interprets your protocol.

因此，将 async def run 更改为 def run 是可行的。