class A:
    def trace(self):
        print("A")

class B(A):
    def trace(self):
        print("B")
        super().trace()

class C(A):
    def trace(self):
        print("C")
        super().trace()

class D(B,C):
    def trace(self):
        print("D")
        super().trace()

D().trace()
#result:
#D
#B
#C
#A