Check for optional return types

[gronke]

As @igalic noted in #83 (comment) the library returns None in functions that do not return an optional type.

def something() -> str:
    # ....
    return None

should be instead

import typing
def something() -> typing.Optional[str]:
    # ...
    return None

[igalic]

i'm kinda upset that mypy isn't catching this

[igalic]

figured out the reason why mypy isn't catching this: we're not asking it to ;)

we could ask it with --strict, or --strict-optional, unfortunately, adding this option would make our tests very sad ;)

we could add it to our travis test-matrix with allow_failure

i have this reproduced & "fixed" here: https://gist.github.com/igalic/b9ab334a8093a35267fb3b77e0f5c09d/revisions

[gronke]

The simplest way to address this is to work on making mypy --strict pass.

[igalic]

"""""simplest""""" way, yes ;)

[gronke]

I did not say the easiest way! But the one we have to think the least about. Or did you give up on full typing coverage? 😏

[igalic]

i did not, it's just very tedious work
fortunately, it's very tedious work that ends up in important redesign (and/or bug fixes) cuz some of the assumptions we made where… shall we say, naïve.

[gronke]

Duplicate of #39