Mypy and Pyright complain when importing new NamedTuple

[gshaikov]

Hi,

I am trying to use generic NamedTuple from the new typing_extensions, however static checkers can't resolve its import.

Below is the code to reproduce and mypy errors as comments.

from typing import TypeVar, Generic

from typing_extensions import NamedTuple  # error: Module "typing_extensions" has no attribute "NamedTuple"

T_co = TypeVar('T_co', covariant=True)

class Foo(NamedTuple, Generic[T_co]):  # error: Class cannot subclass "NamedTuple" (has type "Any")
    bar: T_co

Not sure what the problem is. I see that there's a conditional here that checks for Python 3.11. It might be the case that type checkers can't resolve this statically. This is just a hypothesis though.

Environment

Python 3.8.10

typing_extensions==4.3.0
mypy==0.942

[AlexWaygood]

I forgot to add it to the typeshed stub for typing_extensions -- the stub is all that the type checker sees :) python/typeshed#8295 should fix the issue.

It might be worth noting, however, that mypy doesn't yet support generic NamedTuples (python/mypy#685) -- my typeshed PR will fix the import issue, but mypy will still emit errors if you try to actually use generic NamedTuples. I know pyright supports generic NamedTuples; not sure about pytype and pyre.

[gshaikov]

Great, thanks!

[gshaikov]

@AlexWaygood I see the fix was merged. I think the typeshed CI pipeline already ran too since then. How do I get this stub into my env? Thanks.

[JelleZijlstra]

You have to wait for the next mypy or pyright release. We can probably get this into mypy 0.970 (expected soon), and pyright releases with updated stubs frequently.

[AlexWaygood]

In the meantime, if you're using mypy, one option is to clone typeshed's master branch and use mypy with the --custom-typeshed-dir option. Pyright might have a similar option you can use to override its vendored copy of typeshed, but I'm not sure.

[gshaikov]

Great thanks both!