How to type hint a generator in Python 3?

You need to import the typing module. As per docs:

The return type of generator functions can be annotated by the generic
type Generator[yield_type, send_type, return_type] provided by
typing.py module

Try this way instead:

from typing import Generator


def generate() -> Generator[int, None, None]:
    for i in range(10):
        yield i

The above will have the desired result:

l = [i for i in generate()]

Output:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

As pointed out in the comments, you might not use the last version of PyCharm. Try switching to version 2016.3.2 and you might be fine. Unfortunately this is a well-known bug, as per @AshwiniChaudhary comment.

More, the reported issue (for the last version of PyCharm) was submitted on December, last year. They probably fixed it and pushed the modifications into the same version.