Shared via mypy Playground

main.py

import dataclasses
from functools import partial
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    frozen_nan_safe = dataclasses.dataclass
else:
    frozen_nan_safe = partial(dataclasses.dataclass, frozen=True)
    
def test_frozen_decorator() -> None:
    @frozen_nan_safe
    class Good:
        x: float

    nan = float('nan')
    hash(Good(nan))
    assert Good(nan) == Good(nan)