Python中的super

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本文通过实例详细解析了Python中使用super()方法时的调用顺序变化，包括不同初始化方法顺序对类继承结构的影响。

I had played a bit with super(), and had recognized that we can change calling order.

For example, we have next hierarchy structure:

A
/ \
B C
\ /
D

In this case MRO of D will be (only for Python 3):

In [26]: D.__mro__

Out[26]: (__main__.D, __main__.B, __main__.C, __main__.A, object)

Let's create a class where

In [23]: class A(object): # or with Python 3 can define class A:
...: def __init__(self):
...: print("I'm from A")
...:
...: class B(A):
...: def __init__(self):
...: print("I'm from B")
...: super().__init__()
...:
...: class C(A):
...: def __init__(self):
...: print("I'm from C")
...: super().__init__()
...:
...: class D(B, C):
...: def __init__(self):
...: print("I'm from D")
...: super().__init__()
...: d = D()
...:
I'm from D
I'm from B
I'm from C
I'm from A

A
/ ⇖
B ⇒ C
⇖ /
D

So we can see that resolution order is same as in MRO. But when we call super() in the beginning of the method:

In [21]: class A(object): # or class A:
...: def __init__(self):
...: print("I'm from A")
...:
...: class B(A):
...: def __init__(self):
...: super().__init__() # or super(B, self).__init_()
...: print("I'm from B")
...:
...: class C(A):
...: def __init__(self):
...: super().__init__()
...: print("I'm from C")
...:
...: class D(B, C):
...: def __init__(self):
...: super().__init__()
...: print("I'm from D")
...: d = D()
...:
I'm from A
I'm from C
I'm from B
I'm from D