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

mypy の診断に関係する Awaitable の定義から始め、次に src/twisted/internet/defer.py の 894-920 行付近にある Deferred.iter と await と比較します。宣言された戻り値の型が、報告された代入エラーなしでこのイテレーター実装を受け入れ、関連する型チェックに合格すれば完了です。