避免在子类中​​指定的所有参数 [英] Avoid specifying all arguments in a subclass

问题描述

我有一个类：

class A(object):
    def __init__(self,a,b,c,d,e,f,g,...........,x,y,z)
        #do some init stuff

和我有，需要一个额外的ARG一个子类（最后一个是W ）

And I have a subclass which needs one extra arg (the last W)

class B(A):
    def __init__(self.a,b,c,d,e,f,g,...........,x,y,z,W)
        A.__init__(self,a,b,c,d,e,f,g,...........,x,y,z)
        self.__W=W

这似乎愚蠢写这一切锅炉板code，如通过所有的ARGS从 B 的构造函数到里面调用 A 的构造函数，从此以后每次更改 A 的构造函数必须适用于其他两个地方在乙的code。

It seems dumb to write all this boiler-plate code, e.g passing all the args from B's Ctor to the inside call to A's ctor, since then every change to A's ctor must be applied to two other places in B's code.

我猜测的Python有一些成语来处理这样的案件，我不知道。你能指出我朝着正确的方向吗？

I am guessing python has some idiom to handle such cases which I am unaware of. Can you point me in the right direction?

我最好的预感，就是有一种拷贝构造函数对于A，然后更改B的code到

My best hunch, is to have a sort of Copy-Ctor for A and then change B's code into

class B(A):
     def __init__(self,instanceOfA,W):
         A.__copy_ctor__(self,instanceOfA)
         self.__W=W

给出的父类的实例时这会适合我的需要，因为我总是创建的子类，虽然我不知道它是否是可能的...

This would suit my needs since I always create the subclass when given an instance of the father class, Though I am not sure whether it's possible...

推荐答案

考虑到参数既可以按名称或位置进行传递，我想code：

Considering that arguments could be passed either by name or by position, I'd code:

class B(A):
    def __init__(self, *a, **k):
      if 'W' in k:
        w = k.pop('W')
      else:
        w = a.pop()
      A.__init__(self, *a, **k)
      self._W = w

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