Type annotation "List"[int] generates runtime error but is accepted by mypy

[erictraut]

This bug was just logged against pyright (and fixed): microsoft/pyright#1393

I noticed that mypy also fails to report this error.

from typing import List
foo: "List"[int] = [1] # Accepted by mypy but generates runtime error

[gvanrossum]

FWIW in Python 3.10 this won't be a runtime error any more, so I suppose it's not a high priority.

[erictraut]

Ah, good to know. I'll change the error check to be conditional on the Python version.

[hauntsaninja]

In general, mypy unfortunately doesn't keep track of whether or not a type is quoted / would be evaluated at runtime (we added some support for checking this for PEP 604 syntax use, but that's about it). Linking #948

[JelleZijlstra]

I think Guido was referring to PEP 563 / from __future__ import annotations, which didn't end up being turned on by default in 3.10, so this is a runtime error in 3.10 too.