Декорирование метаклассов. Пример в книге не работает

class Metaclass(type):
    def __new__(meta, clsname, supers, attrdict):
        print('In M.__new__:')
        print([clsname, supers, list(attrdict.keys())])

def decorator(cls):
    return Metaclass(
        cls.__name__,
        cls.__bases__,
        dict(cls.__dict__),
    )

class A:
    x = 1

@decorator
class B(A):
    y = 2
    
    def m(self):
        return self.x + self.y


B.x, B.y

i = B()
i.x, i.y, i.m()

B.x, B.y
(1, 2)

i = B()
i.x, i.y, i.m()
(1, 2, 3)

./test.py
In M.__new__:
['B', (<class '__main__.A'>,), ['__module__', 'y', 'm', '__doc__']]
Traceback (most recent call last):
  File "/home/user/code/./test.py", line 360, in <module>
    B.x, B.y
AttributeError: 'NoneType' object has no attribute 'x'

print(B)
out: None