Invalid Attribute Override

What it does

Detects attribute overrides that change whether an inherited attribute is a class variable or an instance variable.

This rule currently only covers class-variable and instance-variable category changes.

Why is this bad?

Pure class variables and instance variables have different access and assignment behavior. Overriding one with the other violates the Liskov Substitution Principle ("LSP"), because code that is valid for the superclass may no longer be valid for the subclass.

Example

from typing import ClassVar


class Base:
    instance_attr: int
    class_attr: ClassVar[int]


class Sub(Base):
    instance_attr: ClassVar[int]  # error: [invalid-attribute-override]
    class_attr: int  # error: [invalid-attribute-override]