self vs cls

Even though self is the most common name used for the first argument of a method, cls is also used in class methods to refer to the class itself. Python will still pass the class reference as the first argument to the method, but it is a convention to use cls instead of self in class methods.

class Foo:
    x = 0
 
    @classmethod
    def bar(cls):
        cls.x += 1
        print(cls.x)
 
Foo.bar() # 1
Foo.bar() # 2