直接调用__init__的目的是什么? [英] What is the purpose of calling __init__ directly?

问题描述

我很难弄清我遇到的一些代码的用途.

I am having a hard time figuring out the purpose some code that I've come across.

该代码具有一个类Foo，该类具有一个带有多个参数的__init__方法.到目前为止，从我对Python的了解中，通过调用Foo('bar')，它将把此字符串作为参数传递给__init__(我认为应该等效于构造函数).

The code has a class Foo, which has an __init__ method that takes multiple arguments. From what I've learned of Python so far, by calling Foo('bar'), it will pass this string as a parameter to __init__ (which I think is supposed to be the equivalent of a constructor).

但是我遇到的问题是我正在查看的代码正在直接调用Foo.__init__('bar').这样做的目的是什么?我几乎觉得我在__init__后面缺少其他用途.

But the issue I am having is that the code I am looking at is calling Foo.__init__('bar') directly. What is the purpose of this? I almost feel that I am missing some other purpose behind __init__.

推荐答案

实例化一个类时，将为您调用__init__()方法.但是，父类中的__init__()方法不会自动调用，因此如果要扩展其功能，则需要直接调用它:

The __init__() method gets called for you when you instantiate a class. However, the __init__() method in a parent class doesn't get called automatically, so need you to call it directly if you want to extend its functionality:

class A:

     def __init__(self, x):
          self.x = x

class B(A):

     def __init__(self, x, y):
          A.__init__(self, x)
          self.y = y

请注意，上述调用也可以使用 super 编写em> :

Note, the above call can also be written using super:

class B(A):

     def __init__(self, x, y):
          super().__init__(x)
          self.y = y

__init__()方法的用途用于初始化类.它通常负责填充实例变量.因此，您希望对类层次结构中的所有类调用__init__().

The purpose of the __init__() method is to initialize the class. It is usually responsible for populating the instance variables. Because of this, you want to have __init__() get called for all classes in the class hierarchy.

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