no-self-use (PLR6301)

Preview (since v0.0.286) · Related issues · View source

Derived from the Pylint linter.

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

What it does

Checks for the presence of unused self parameter in methods definitions.

Why is this bad?

Unused self parameters are usually a sign of a method that could be replaced by a function, class method, or static method.

This rule exempts methods decorated with @typing.override. Converting an instance method into a static method or class method may cause type checkers to complain about a violation of the Liskov Substitution Principle if it means that the method now incompatibly overrides a method defined on a superclass. Explicitly decorating an overriding method with @override signals to Ruff that the method is intended to override a superclass method and that a type checker will enforce that it does so; Ruff therefore knows that it should not enforce rules about unused self parameters on such methods.

Example

class Person:
    def greeting(self):
        print("Greetings friend!")

Use instead:

def greeting():
    print("Greetings friend!")

or

class Person:
    @staticmethod
    def greeting():
        print("Greetings friend!")