如何正确为AsyncGenerator、AsyncContextManager指定类型提示修复mypy报错

该报错不属于mypy本身的问题，是类型签名不匹配导致的：

contextlib.asynccontextmanager装饰器的作用是将一个单次yield的异步生成器函数，包装为返回异步上下文管理器的函数。被装饰的函数本身的返回值是AsyncIterator[T]，但装饰后的方法实际调用时返回的是AsyncContextManager[T]，你在子类方法上写的是装饰前的函数返回类型，自然和父类要求的AsyncContextManager类型不匹配。

直接将子类subscribe方法的返回类型调整为和父类完全一致即可，mypy会自动识别asynccontextmanager装饰器的类型转换逻辑：

import contextlib
import abc
import asyncio

from typing import AsyncContextManager, AsyncGenerator, AsyncIterator


class Base:
    @abc.abstractmethod
    async def subscribe(self) -> AsyncContextManager[AsyncGenerator[int, None]]:
        pass

class Impl1(Base):
    @contextlib.asynccontextmanager
    async def subscribe(self) -> AsyncContextManager[AsyncGenerator[int, None]]:
        async def _generator():
            for i in range(5):
                await asyncio.sleep(1)
                yield i
                    
        yield _generator()

如果觉得类型太长可读性差，可以定义类型别名统一管理：

from typing import TypeAlias

SubscribeResult: TypeAlias = AsyncGenerator[int, None]
SubscribeReturn: TypeAlias = AsyncContextManager[SubscribeResult]

class Base:
    @abc.abstractmethod
    async def subscribe(self) -> SubscribeReturn:
        pass

class Impl1(Base):
    @contextlib.asynccontextmanager
    async def subscribe(self) -> SubscribeReturn:
        async def _generator():
            for i in range(5):
                await asyncio.sleep(1)
                yield i
                    
        yield _generator()

内容的提问来源于stack exchange，提问作者Andreas H.