import types

class ClassOrInstanceMethod(object):
    def __init__(self, wrapped):
        self.wrapped = wrapped
    def __get__(self, instance, owner):
        if instance is None:
            instance = owner
        return self.wrapped.__get__(instance, owner)

class demo(object):
    @ClassOrInstanceMethod
    def foo(self):
        # self will be the class if this is called on the class
        print(self)

demo.foo()
demo().foo()