Currently typing.Generator requires three arguments: Generator[YieldType, SendType, ReturnType].

At least for me, passing values to a generator is a very rare case. I suggest to allow only one argument to be passed to Generator: Generator[YieldType], where the other arguments default to None. This makes the common case more readable and is less error-prone. (I always forget the second and third argument, since that use case is so uncommon for me.)