def wrap(cls):
    print("In wrap() for class %s" % cls.__name__)
    name = cls.__name__
    class Wrapper(cls):
        def __init__(self, *args, **kwargs):
            print("In Wrapper(%s).__init__()" % name)
            super().__init__(*args, **kwargs)
    return Wrapper

class Metaclass(type):
    def __new__(meta, name, bases, namespace):
        print("In Metaclass.__new__() for class %s" % name)
        cls = super().__new__(meta, name, bases, namespace)
        return cls if cls.__name__ == 'Wrapper' else wrap(cls)

class A(metaclass = Metaclass):
    def __init__(self):
        print("In A.__init__()")
        super().__init__()

@wrap
class B:
    def __init__(self):
        print("In B.__init__()")
        super().__init__()

print(A.mro())
print(B.mro())

B() # Works
A() # Loops in A.__init__()