Awaitable.__await__ expects a Generator where an Iterator will do

In Twisted, the Deferred class has set __await__ = __iter__, where __iter__ is typed thusly:

    def __iter__(self) -> "Deferred[_DeferredResultT]":

Deferred, insofar as it has an __iter__ method, is thus itself an Iterable. It also implements __next__, so is an Iterator.

Mypy is yielding this error:

src/twisted/internet/defer.py:919:17: error: Incompatible types in assignment (expression has type "Callable[[], Deferred[_DeferredResultT]]", base class "Awaitable" defined the type as
"Callable[[], Generator[Any, None, _DeferredResultT]]")  [assignment]

I suspect that perhaps Awaitable.__await__ could instead be more flexibly typed to return a Iterator[_T] instead of a Generator[Any, None, _T]… as that (a) seemingly works in this case and (b) the documentation for object.__await__ and PEP 492 say that it must return an iterator and not specifically a generator.

Deferred: mypy problem: https://github.com/python/typeshed/pull/5194#issuecomment-816339179

从 mypy 诊断中涉及的 Awaitable 定义开始，然后将其与 src/twisted/internet/defer.py 中约第 894-920 行的 Deferred.iter 和 await 进行比较。当声明的返回类型能够接受此迭代器实现而不会出现所报告的赋值错误，并且相关类型检查通过时，即视为完成。