当父类有一个 super() 是什么意思? [英] What does it mean when a parent class has a super()?

问题描述

据我所知，super()用于调用子类中覆盖的方法(就像子类中覆盖的__init__).

As far as i know, super() is used to call the methods overwritten in the subclass (like an overwritten __init__ in the subclass).

另外，我知道所有 python 类都继承自一个名为 object 的特殊类.

Also, i know that all python classes inherit from a special class called object.

在学习 OOP 时，我遇到了一个奇怪的例子:

While studying OOP i ran into a weird example:

class A(object):
    def __init__(self):
        print('A.__init__')
        super().__init__()

class B(object):
    def __init__(self):
        print('B.__init__')
        super().__init__()

class C(A, B):
    def __init__(self):
        print('C.__init__')
        super().__init__()

我理解大部分内容，除了...为什么A类有一个super().__init__()?它是父类，它不需要从任何人那里继承.特殊的 object 类不做任何事情，所以我不知道为什么需要它.

I understand most of this except...why does class A has a super().__init__()? It's the parent class, it shouldn't need to inherit from anyone. And the special object class doesn't do anything so i don't know why it would need it.

这不是我在父类中看到 super 的唯一案例，在我之前提出的一个问题中，一个问题的解决方案涉及它，但我不明白.我也找不到对 super() 继承的这种用法的简单解释.

This is not the only case i have seen a super in the parent class, in a previous question i made, a solution to aproblem involved it but i didn't understood it. I also can't find an easy explanation of this usage of super() inheritance.

简单来说...为什么我需要在父类中使用 super() ?

In simple terms...why would i need to use super() in a parent class?

推荐答案

考虑以下示例:

class A:
    def __init__(self, a, **kwargs):
        print('A.__init__ called')
        self.a = a
        super().__init__(**kwargs)
        print('A.__init__ finished')

class B:
    def __init__(self, b, **kwargs):
        print('B.__init__ called')
        self.b = b
        super().__init__(**kwargs)
        print('B.__init__ finished')

class C(A, B):
    def __init__(self, c, **kwargs):
        print('C.__init__ called')
        self.c = c
        super().__init__(**kwargs)
        print('C.__init__ finished')

当你创建一个C对象时，输出如下:

When you create a C object, the output is as follows:

>>> C(a=1, b=2, c=3)
C.__init__ called
A.__init__ called
B.__init__ called
B.__init__ finished
A.__init__ finished
C.__init__ finished
<__main__.C object at 0x7fd15abcab70>

从__init__方法的调用顺序，以及它们以相反的顺序结束的事实，我们可以看到C.__init__ 调用 A.__init__，后者调用 B.__init__.也就是说，虽然 A 没有显式的父类(所以它的直接父类是 object)，super().__init__ 在 中调用>A 实际上调用了 B.__init__.

From the order that the __init__ methods are called, and the fact that they finish in reverse order, we can see that C.__init__ calls A.__init__, which calls B.__init__. That is, although A has no explicit parent class (so its direct parent is object), the super().__init__ call in A actually calls B.__init__.

这是因为B是C的方法解析顺序 (MRO).A类需要调用super()，因为虽然它的超类是object，但是Python允许多重继承，所以A> 不能保证它是 MRO 中 object 之前的最后一个类.

This is because B is the next class after A in C's method resolution order (MRO). The A class needs to call super() because although its superclass is object, Python allows multiple inheritance, so A cannot guarantee that it is the last class before object in the MRO.

>>> C.__mro__
(<class '__main__.C'>, <class '__main__.A'>, <class '__main__.B'>, <class 'object'>)

参见 Raymond Hettinger 的文章 Python 的 super() 考虑super! 有关 MRO 和协作多继承技术"的更详细说明.

See Raymond Hettinger's article Python's super() considered super! for a more detailed explanation about the MRO and "cooperative multiple inheritance techniques".

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