Repository navigation
False positive: Final dataclass field with type variable #22396
Description
Bug Report
When using a dataclass with a field defined using Final and containing a type variable, mypy incorrectly errors because it infers the field as a class variable.
To Reproduce
from dataclasses import dataclass
from typing import Final
@dataclass
class Wrapper[T]:
obj: Final[T]https://gist.github.com/mypy-play/edaf1efd9e1fec0e7b89e68b17ffae6e
Expected Behavior
No errors, the check does not apply to dataclasses.
Actual Behavior
main.py:6: error: Final name declared in class body cannot depend on type variables [misc]
Found 1 error in 1 file (checked 1 source file)
Note: mypy does correctly infer that the field is a readonly generic instance attribute, but this is a separate, specific error that should exempt dataclasses.
Simply suppressing the specific misc error leads to desired behavior.
Your Environment
- Mypy version used: 2.4.1
- Mypy command-line flags: N/A
- Mypy configuration options from
mypy.ini(and other config files): N/A - Python version used: 3.12
Activity
[-]False positive: Final dataclass field[/-][+]False positive: Final dataclass field with type variable[/+]nilayp-codes commentedon Nov 8, 2026
I’d like to work on this. The error comes from the DEPENDENT_FINAL_IN_CLASS_BODY check in TypeChecker.visit_assignment_stmt (mypy/checker.py), which doesn’t account for dataclass fields. Those are instance attributes, and the dataclass plugin already allows bare Final[...] fields. I’m planning to skip the check for classes processed by the dataclass plugin and add a test case to check-dataclasses.test.
ilevkivskyi commentedon Nov 8, 2026
This is essentially a duplicate of #21637
Finalattributes using typevars in dataclasses #21637