self-or-cls-assignment (PLW0642)

Derived from the Pylint linter.

What it does

Checks for assignment of self and cls in instance and class methods respectively.

Why is this bad?

The identifiers self and cls are conventional in Python for the first parameter of instance methods and class methods, respectively. Assigning new values to these variables can be confusing for others reading your code; using a different variable name can lead to clearer code.

Example

class Version:
    def add(self, other):
        self = self + other
        return self

    @classmethod
    def superclass(cls):
        cls = cls.__mro__[-1]
        return cls

Use instead:

class Version:
    def add(self, other):
        new_version = self + other
        return new_version

    @classmethod
    def superclass(cls):
        supercls = cls.__mro__[-1]
        return supercls