classmethod.txt

@classmethod in python

A class method receives the class as implicit first argument, just like an instance method receives the instance. To declare a class method, use this idiom:

class C(object):
    @classmethod
    def f(cls, arg1, arg2, ...):
        ...


From stack overflow:
The most straightforward way to think about it is to think in terms of what type of object the method needs in order to do its work. 

If your method needs access to an instance, make it a regular method. 

If it needs access to the class, make it a classmethod. 

If it doesn't need access to the class or the instance, but is thematically related to the class (typical example: make_from methods) then use staticmethod.

Otherwise, make it a module function.