How can I access a classmethod from inside a class in Python

Question

I would like to create a class in Python that manages above all static members. These members should be initiliazed during definition of the class already. Due to the fact t

Answer 1

You can't call a classmethod in the class definition because the class hasn't been fully defined yet, so there's nothing to pass the method as its first cls argument...a classic chicken-and-egg problem. However you can work around this limitation by overloading the __new__() method in a metaclass, and calling the classmethod from there after the class has been created as illustrated below:

class Test(object):
    # nested metaclass definition
    class __metaclass__(type):
        def __new__(mcl, classname, bases, classdict):
            cls = type.__new__(mcl, classname, bases, classdict)  # creates class
            cls.static_init()  # call the classmethod
            return cls

    x = None

    @classmethod
    def static_init(cls):  # called by metaclass when class is defined
        print("Hello")
        cls.x = 10

print Test.x

Output:

Hello
10