Python inherit and super

2017/01/16

Tags: python super inherit

又学习了一个 python 的继承。有很多帖子都有介绍,比如理解 Python superpython super()

先看一个例子,这个是第一个文章里面的。

class Root(object):
    def __init__(self):
        print("this is Root")


class B(Root):
    def __init__(self):
        print("enter B")
        super(B, self).__init__()
        print("leave B")


class C(Root):
    def __init__(self):
        print("enter C")
        super(C, self).__init__()
        print("leave C")


class D(C):
    def __init__(self):
        print("enter D")
        super(D, self).__init__()
        print("leave D")


class E(D, B):
    def __init__(self):
        print("enter E")
        super(E, self).__init__()
        print("leave E")

e = E()
print(e.__class__.mro())

# results:
# enter E
# enter D
# enter C
# enter B
# this is Root
# leave B
# leave C
# leave D
# leave E
# [<class '__main__.E'>, <class '__main__.D'>, <class '__main__.C'>, <class '__main__.B'>, <class '__main__.Root'>, <class 'object'>]

没有什么问题,所有的类都做了初始化,很完美。接着再看一个例子,这个例子其实是上面第二篇文章里面的。

class A(object):
    def __init__(self):
        print("enter A")
        print("leave A")


class B(object):
    def __init__(self):
        print("enter B")
        print("leave B")


class C(A):
    def __init__(self):
        print("enter C")
        super(C, self).__init__()
        print("leave C")


class D(A):
    def __init__(self):
        print("enter D")
        super(D, self).__init__()
        print("leave D")


class E(B, C):
    def __init__(self):
        print("enter E")
        super(E, self).__init__()
        print("leave E")


class F(E, D):
    def __init__(self):
        print("enter F")
        super(F, self).__init__()
        print("leave F")


f = F()
print(f.__class__.mro())

# results:
# enter F
# enter E
# enter B
# leave B
# leave E
# leave F
# [<class '__main__.F'>, <class '__main__.E'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.D'>, <class '__main__.A'>, <class 'object'>]

我发现和文章里面贴的结果不一样,里面缺少对 C,D,A 的初始化。琢磨半天才弄明白,主要原因就是,AB 其实也是继承自 object,然而我们并没有调用 super 来初始化,所以只需要加上就可以了。

class A(object):
    def __init__(self):
        print("enter A")
        super(A, self).__init__()
        print("leave A")


class B(object):
    def __init__(self):
        print("enter B")
        super(B, self).__init__()
        print("leave B")


class C(A):
    def __init__(self):
        print("enter C")
        super(C, self).__init__()
        print("leave C")


class D(A):
    def __init__(self):
        print("enter D")
        super(D, self).__init__()
        print("leave D")


class E(B, C):
    def __init__(self):
        print("enter E")
        super(E, self).__init__()
        print("leave E")


class F(E, D):
    def __init__(self):
        print("enter F")
        super(F, self).__init__()
        print("leave F")


f = F()
print(f.__class__.mro())

# results:
# enter F
# enter E
# enter B
# enter C
# enter D
# enter A
# leave A
# leave D
# leave C
# leave B
# leave E
# leave F
# [<class '__main__.F'>, <class '__main__.E'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.D'>, <class '__main__.A'>, <class 'object'>]

这样就完美了。目测这个会是一个隐藏的坑。

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