dataclasses_frozen error

Assignment to attribute of a frozen dataclass instance, or invalid frozen/non-frozen dataclass inheritance

@dataclass(frozen=True) instances are immutable — their attributes cannot be reassigned after construction. Additionally, a frozen dataclass cannot inherit from a non-frozen one, and vice versa.

@dataclass(frozen=True)
class Point:
    x: float

p = Point(1.0)
p.x = 2.0  # E: dataclass is frozen

@dataclass          # E: non-frozen cannot inherit from frozen
class Sub(Point):
    pass

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial dataclasses_frozen down per-file or per-path from your editor or pyproject.toml, or fix the code so it type-checks. See the Type System rules and the complete diagnostic reference.

Canonical URL: https://www.basilisk-python.dev/errors/dataclasses_frozen