redefined-slots-in-subclass (PLW0244)

Derived from the Pylint linter.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for a re-defined slot in a subclass.

Why is this bad?

If a class defines a slot also defined in a base class, the instance variable defined by the base class slot is inaccessible (except by retrieving its descriptor directly from the base class).

Example

class Base:
    __slots__ = ("a", "b")


class Subclass(Base):
    __slots__ = ("a", "d")  # slot "a" redefined

Use instead:

class Base:
    __slots__ = ("a", "b")


class Subclass(Base):
    __slots__ = "d"