rewrite Generator[..., None, None] to Iterator[...]

[carljm]

No description provided.

[gvanrossum]

Note that these aren't fully equivalent. Generators have a close() method but iterators don't.

[carljm]

Hmm, good point. Perhaps that ought to be mentioned at http://mypy.readthedocs.io/en/latest/kinds_of_types.html#generators ?

In practice (at least in our codebase) I find the close() method to be rarely/never used, and Iterator[Foo] is much nicer on the eyes than Generator[Foo, None, None]. So I'd still be inclined to provide this (and probably even enable it by default). But this difference is certainly worth a mention in the docs. (It would be provided as a TypeRewriter, so if someone doesn't want it, it'd just be a small config change.)

[gvanrossum]

Yeah, that's fine. I was just sensitized to the difference by python/typeshed#1806 (where the key point was that the docs promised a generator so the close() call should be allowed). Can you submit a PR for the mypy docs?

[carljm]

Done: python/mypy#4424

[iyanuashiri]

Hey @carljm, I want to work on this issue. I have gone through the source code and saw a make_generator function. Is my job to change the return value from Generator[..] to Iterator[..]?

Thank you as you reply

[carljm]

Hi @iyanuashiri! Thanks for your interest. We could implement this feature by returning Iterator[yield_type] from make_generator in the case where send_type and return_type are both None. However, given the above discussion I don't think we should do that, because we want to make it easy for someone to opt-out of the rewriting. So instead we should provide this as a TypeRewriter class with a visit_Generator method that inspects the __args__ of the Generator type and rewrites it if the send and return types are None. And then add this new Rewriter to the default rewriter.

[iyanuashiri]

I think I understand what you want me to do. So I should create a class that inherits from TypeRewriter, with a visit_Generator method that inspects the __args__ of the Generator type?

[carljm]

Yes, that’s right!

[iyanuashiri]

Hey @carljm, I am sorry it is taking long to send a pull request. I just got a hang of your code and how to implement my solution. Initially I understood what to do but I didn't know how to do it. I will send a PR as soon as possible. Thank you for the patience.

[kevinjqliu]

TypeRewriter class with a visit_Generator

@carljm I'm confused by the naming convention. Wouldn't we want to name the new method something like rewrite_Generator because the rewrite method in TypeRewriter class will delegate to getattr(typ, 'name', None).

[carljm]

@kevinjqliu Yes, you're right, that was just me mis-remembering the API. I meant rewrite_Generator, not visit_Generator.