`get_type_hints` fails with `NameError` for local types with `__future__` annotations

[francois-rozet]

Copied from python/mypy_extensions#73.

The following code crashes, but only if importing annotations. Tested with Python 3.12, 3.13 and 3.14.

from __future__ import annotations

from typing import get_type_hints


def f():
    class X:
        pass

    class Y:
        x: X

    print(get_type_hints(Y))


f()  # NameError: name 'X' is not defined

from typing import get_type_hints


def f():
    class X:
        pass

    class Y:
        x: X

    print(get_type_hints(Y))


f()  # prints {'x': <class '__main__.f.<locals>.X'>}

[srittau]

@JelleZijlstra @AlexWaygood Could one of you move this to python/cpython?

[andresliszt]

According with get_type_hints docs, with from __future__ import annotations, all annotations are stored as strings (postponed evaluation), get_type_hints must evaluate those strings, calling eval. For classes, default evaluation is:

• module globals (the module where the class lives), and
• the class namespace.

In your code, X lives in the function’s local scope (because both X and Y are defined inside f), not in the module globals or the class namespace.

This code works

from __future__ import annotations

from typing import get_type_hints
import annotationlib

def f():
    class X:
        pass

    class Y:
        x: X

    print(get_type_hints(Y, localns=locals()))

Question is, is this the expected behavior?

[francois-rozet]

Given that the issue only happens when importing annotations, i believe the expected behavior is that it keeps working.

In addition, if a library uses get_type_hints under the hood, it is not possible to provide the locals for the user.

[JelleZijlstra]

I'm pretty sure there have been several duplicates for this already, please search the issue tracker.

The short answer is that from __future__ import annotations is on its way to deprecation (PEP-749) and stringifying annotations inherently makes it impossible to resolve them in all cases. If you want reliable get_type_hints(), don't use from __future__ import annotations.