error: Missing type parameters for generic type "array"

[sg495]

Bug Report

Mypy strict mode complains if a type parameter is omitted when using the built-in array type in an annotation, while Python raises TypeError if a type parameter is included. Mypy only complains in strict mode.

To Reproduce

from array import array
x: array = array("L")      # Mypy error: Missing type parameters for generic type "array"
y: array[int] = array("L") # TypeError: 'type' object is not subscriptable

Expected Behavior

Mypy strict mode should not complain about a missing generic type parameter (since Python does not allow it).

Actual Behavior

array-mypy.py:2: error: Missing type parameters for generic type "array"

Possible Workaround

from array import array
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    IntArray = array[int]
else:
    IntArray = array

x: IntArray = array("L")

Your Environment

• Mypy version used: mypy 0.982 (compiled: yes)
• Mypy command-line flags: mypy --strict
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.9.13

[JelleZijlstra]

See https://mypy.readthedocs.io/en/stable/runtime_troubles.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime for general guidance.

However, in this case we should probably make array support __class_getitem__ at runtime. I can't find a reason why we didn't do that before. I'll submit an issue to CPython to make that change, but it won't be released until 3.12.