Type hinting generator in python 3.6

Question

According to PEP-484 , we should be able to type hinting a generator function as follows:

from typing import Generator

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

for i in generate():
    print(i)

However, the list comprehension gives the following error in PyCharm.

Expected 'collections.Iterable', got 'Generator[int, None, None]' instead less... (⌘F1)

Any idea why PyCharm is considering this as error? Thank you.

---

A few clarification after reading some answers. I am using PyCharm Community Edition 2016.3.2 (the latest version) and have imported the typing.Generator (updated in the code). The above code runs just fine, but PyCharm considers this an error:

So, I'm wondering if this is actually an error or an unsupported feature in PyCharm.

Answer 1

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.

Answer 2

As commented by Oleksandr Dashkov , I tried the same code with Pycharm 2017.1 EAP, which handles this annotation correctly. I guess this feature will be integrated in the next official version of PyCharm. Thanks to everyone.