classes_override_3 error

@override on a method with no matching ancestor method

PEP 698 — a method decorated @override (or typing.override) must actually override a method declared in a base class. When no ancestor declares a method of that name, the decorator is a lie and the type checker should report it.

To stay free of false positives the check is deliberately conservative: it only fires when the entire ancestor chain is resolvable within the current module (no Any base and no imported base whose methods we cannot see), so a method that legitimately overrides something in an unseen base is never flagged.

class Base:
    def existing(self) -> int: ...

class Child(Base):
    @override
    def missing(self) -> int:  # E0159: nothing named `missing` in any base
        return 1

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial classes_override_3 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/classes_override_3