8000 [mypy] Allow variable typed `type[T]` as generic type variable · Issue #11636 · pydantic/pydantic · GitHub
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[mypy] Allow variable typed type[T] as generic type variable #11636

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Closed
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ROCKTAKEY opened this issue Mar 27, 2025 · 1 comment
Closed
3 of 13 tasks

[mypy] Allow variable typed type[T] as generic type variable #11636

ROCKTAKEY opened this issue Mar 27, 2025 · 1 comment
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@ROCKTAKEY
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Initial Checks

  • I have searched Google & GitHub for similar requests and couldn't find anything
  • I have read and followed the docs and still think this feature is missing

Description

For pydantic, generic type information is needed at runtime. Thus, we must recieve type as a function argument and pass as generic type to create generic pydantic model. However, the code bellow causes error on mypy:

from pydantic import BaseModel


class C[T](BaseModel): ...


def f[T](t: type[T]) -> C[T]:
    return C[t]()  # b.py:8: error: Variable "t" is not valid as a type  [valid-type]

This issue is also known on mypy, because pyright does not cause this error, though mypy does not fix it for a long time.

Probably, this problem occurs only with libraries using generic type at runtime, such as Pydantic. I think a solution with the mypy plugin provided by pydantic could be considered.

I'm sorry if it is impossible, I do not know much about mypy plugin limitation.

Thanks!

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@Viicos
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Viicos commented Mar 28, 2025

I think a solution with the mypy plugin provided by pydantic could be considered.

It is not the job of the Pydantic plugin to fix non Pydantic-related issues. It is probably also not be possible to do so, as the mypy plugin interface exposes limited capabilities, and this issue is probably present in mypy's core logic.

@Viicos Viicos closed this as not planned Won't fix, can't repro, duplicate, stale Mar 28, 2025
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