class A(type):
    def __setattr__(self, name, value):
        print("From metaclass: ", name)

class B(metaclass= A):
    def __init__(self): pass

    def __setattr__(self, name, value):
        print("From B: ", name)
        object.__setattr__(self, name, value)

obj = B()
obj.t = 4
print("Value of t is set and it is: ", obj.t)
B.r = 3  #<--- how to initialize this?