bpo-41249: Fix postponed annotations for TypedDict

[Kronuz]

Summary:

This fixes TypedDict to work with get_type_hints() and postponed evaluation of annotations across modules.

This is done by adding the module name to ForwardRef at the time the object is created and using that to resolve the globals during the evaluation.

Test Plan:

Having these two file:

# foo.py
from __future__ import annotations

from typing import Optional, TypedDict

class Foo(TypedDict):
    a: Optional[int]

# bar.py
from __future__ import annotations

from typing import get_type_hints
from foo import Foo

class Bar(Foo, total=False):
    b: int

print(get_type_hints(Bar))

Before:

$ python bar.py
Traceback (most recent call last):
  File "/Users/kronuz/Development/cpython/bar.py", line 9, in <module>
    print(get_type_hints(Bar))
  File "/Users/kronuz/Development/cpython/Lib/typing.py", line 1724, in get_type_hints
    value = _eval_type(value, base_globals, base_locals)
  File "/Users/kronuz/Development/cpython/Lib/typing.py", line 317, in _eval_type
    return t._evaluate(globalns, localns, recursive_guard)
  File "/Users/kronuz/Development/cpython/Lib/typing.py", line 660, in _evaluate
    eval(self.__forward_code__, globalns, localns),
  File "<string>", line 1, in <module>
NameError: name 'Optional' is not defined

After:

$ python bar.py
{'a': typing.Optional[int], 'b': <class 'int'>}

https://bugs.python.org/issue41249

[Fidget-Spinner]

Thanks for submitting this fix! Some general comments:

• Please add your proposed tests. Tests for typing are at https://github.com/python/cpython/blob/main/Lib/test/test_typing.py. Since your tests require multiple files, you can create them in that folder, or reuse this file that's used for testing type annotations in separate modules https://github.com/python/cpython/blob/main/Lib/test/mod_generics_cache.py)
• Please add a news entry via blurb.

I'll try to do a full review later.

[Kronuz]

@Fidget-Spinner, I added the tests, the news entry and fixed the KeyError as suggested. Thank you!

[Fidget-Spinner]

LG in general! I just have a few non-code comments. Thanks :).

[Fidget-Spinner]

LGTM. Thanks for the quick response!

Please don't force push in the future. It overwrites valuable history, and besides, the core devs will squash and merge your PR as a single commit :).

I can't merge your PR, so I'll wait for Guido or some other core dev to review. If no one tends to this in a week or two, please gently ping the issue tracker.

[Kronuz]

@Fidget-Spinner, I made the suggested changes. Thank you for reviewing! 😃

[gvanrossum]

LG except I'd like the helper module renamed. Thanks!

[septatrix]

I still think it would be beneficial to figure out why TypedDicts have no MRO as this would trivially solve this problem. That being said I think this is a rather clean workaround for the time being

[gvanrossum]

Just one nit, I’ll commit the fix and then land.

[Fidget-Spinner]

@Kronuz congrats on landing your first PR in CPython :)! Great work!

[gvanrossum]

Yes, good work!

[miss-islington]

Thanks @Kronuz for the PR, and @gvanrossum for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[miss-islington]

Thanks @Kronuz for the PR, and @gvanrossum for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

[miss-islington]

Sorry, @Kronuz and @gvanrossum, I could not cleanly backport this to 3.9 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 889036f7ef7290ef15b6c3373023f6a35387af0c 3.9

[miss-islington]

Sorry @Kronuz and @gvanrossum, I had trouble checking out the 3.10 backport branch.
Please backport using cherry_picker on command line.
cherry_picker 889036f7ef7290ef15b6c3373023f6a35387af0c 3.10

[Fidget-Spinner]

I'll look into it.

[miss-islington]

Thanks @Kronuz for the PR, and @gvanrossum for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

[Fidget-Spinner]

Seems like bedevere was just feeling a little unwell ;).