ruff/docs/rules/missing-type-cls.md

missing-type-cls (ANN102)

Derived from the flake8-annotations linter.

What it does

Checks that class method cls arguments have type annotations.

Why is this bad?

Type annotations are a good way to document the types of function arguments. They also help catch bugs, when used alongside a type checker, by ensuring that the types of any provided arguments match expectation.

Note that many type checkers will infer the type of cls automatically, so this annotation is not strictly necessary.

Example

class Foo:
    @classmethod
    def bar(cls):
        ...

Use instead:

class Foo:
    @classmethod
    def bar(cls: Type["Foo"]):
        ...