BSK-E0077 error

Protocol Self-return conformance violation

When a Protocol declares a method returning Self, any class passed where that protocol is expected must have the corresponding method return Self or the class itself. If the method returns a completely different type (e.g. int or a different class), the class does not satisfy the protocol.

class ShapeProtocol(Protocol):
    def set_scale(self, scale: float) -> Self: ...

class BadReturn:
    def set_scale(self, scale: float) -> int:
        return 42

def accepts(s: ShapeProtocol) -> None: ...

def main(bad: BadReturn) -> None:
    accepts(bad)  # E — BadReturn.set_scale returns int, not Self

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial BSK-E0077 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/BSK-E0077