What would the use of Union[int, NoReturn] be? We could type functions that either return int or throw an exception (e.g., the int constructor) this way, but I'm not sure that would enable better type checking.

Callable[..., NoReturn] makes more logical sense to me, but it doesn't seem like something that's often useful in practice.

I think we've learned in the past that typing.py should be kept simple, stupid. A static checker can reject List[NoReturn].

@gvanrossum

I think we've learned in the past that typing.py should be kept simple, stupid.

Yes, right :-) Since this case is not obvious, we can let type checkers decide.

Code LGTM. I wonder though if we should get Mark Shannon's view of the PEP 484 changes first.

There is no hurry with this (this could not go into 3.6.1), let us first sort out the PEP, and then I could merge this.

Feel free to merge as soon as 3.6.1 is released. (And typing 3.6.1 has been pushed to PyPI.)