python 3类继承问题

Question

class A(object):
    def __init__(self):
        self.a = 1

class B(A):
    def __init__(self):
        A.__init__(self)
        self.a = 2
        self.b = 3


class C(object):
    def __init__(self):
        self.a = 4
        self.c = 5

class D(C, B):
    def __init__(self):
        C.__init__(self)
        B.__init__(self)
        self.d = 6

obj = D()
print(obj.a)

My understanding is that python will first search class C then B then A to get a. So print(obj.a) will print out 4 when searching class C. But the answer is 2. This means that Python got self.a = 2 from class B instead of self.a = 4 from class C. Can anyone explain the reasons? Thank you

Answer 1

There is no search going on here. You are making explicit, direct calls to unbound methods, passing in self manually. These are simple function calls , nothing more.

So this is just a question of tracing the execution order:

D() -> D.__init__(self)
    C.__init__(self)
        self.a = 4
    B.__init__(self)
        A.__init__(self)
            self.a = 1
        self.a = 2

So a is assigned 4 , then 1 , then 2 .