Class method

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Class method#

A class method is a method that takes the class itself as its first argument (typically named cls). It should be defined using the classmethod decorator. A crucial feature of a class method is that it can be called not only from an instance of the class (like a typical method) but also directly from the class itself.

Inheritance#

The question is: does cls refer to the ancestor (the class where the method is defined) or the descendant (the class from which the method is called)? In Python, cls always refers to the descendant—the class on which the method is invoked—regardless of whether the method is inherited or overridden.

The following example defines the Base class, which has a class method that allows us to identify the class we are operating on.

class Base:
    @classmethod
    def example_method(cls):
        return cls

The following code is really obvious, as we call exmpale_method from Desc1 itself, which was passed to the cls argument.

class Desc1(Base):
    pass

Desc1.example_method()

__main__.Desc1

More specific case refers to calling example_method from super.

class Desc2(Base):
    @classmethod
    def example_method(cls):
        return super().example_method()

Desc2.example_method()

__main__.Desc2

But the result is the same - cls still refers to the class from which the method was called.

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