def classDecorator(cls):
    class NewClass(cls):
        def extraMethod(self):
            print("decorator-added method",self.__class__.__name__)
    return NewClass


@classDecorator
class FooBar(object):
    def __init__(self):
        self.bar = "baz"
    def myMethod(self):
        print(self.bar)


let l = FooBar()
l.extraMethod()
l.myMethod()