Python copy：如何继承默认复制行为？ [英] Python copy : How to inherit the default copying behaviour?

问题描述

好吧...这可能是一个愚蠢的问题...但我现在没有找到答案！

我需要实现对象，我想要复制所有的属性，除了一个或两个我想完全控制副本。

这是标准的复制行为对象：

 >>> class test（object）：
 ... def __init __（self，arg）：
 ... self._a = arg 
 ... 
>>> t = test（123999）
>>>> t._a 
 123999 
>>>> tc = copy.copy（t）
>>>> tc._a 
 123999 
  

这基本上意味着复制所有属性。我想做的是以下列方式重用此行为：

 >> class test（object）：
 ... def __init __（self，arga，argb）：
 ... self._a = arga 
 ... self._b = argb 
 ... 
 ... def __copy __（self）：
 ... obj_copy = copy.copy（self）#NOT POSSIBLE OF COURSE =>无限递归
 ... obj_copy._b = my_operation（obj_copy._b）
 ... return obj_copy 
  

我希望你知道点：我想重用对象复制行为，但钩住我自己的操作。是否有一个干净的方式来做到这一点（不必在 c>

$ <

  def __copy __（self） ：
 clone = copy.deepcopy（self）
 clone._b = some_op（clone._b）
返回clone 
  

这将工作，因为 deepcopy 避免递归。从 python文档：

deepcopy（）函数通过以下方式避免了这些问题：
保持在当前复制过程中已经复制的对象的memo字典;和
让用户定义的类重写复制操作或复制的组件集。

Ok ... It might be a stupid question ... but I'm not finding the answer right now !

I need to realize the copy of an object, for which I want all the attributes to be copied, except one or two for which I want to fully control the copy.

Here is the standard copying behaviour for an object :

>>> class test(object):
...     def __init__(self, arg):
...         self._a = arg
... 
>>> t = test(123999)
>>> t._a
123999
>>> tc = copy.copy(t)
>>> tc._a
123999

Which basically means that all the attributes are copied. What I would like to do is re-use this behaviour in the following way :

>>> class test(object):
...     def __init__(self, arga, argb):
...         self._a = arga
...         self._b = argb
...
...     def __copy__(self):
...         obj_copy = copy.copy(self) #NOT POSSIBLE OF COURSE => infinite recursion
...         obj_copy._b = my_operation(obj_copy._b)
...         return obj_copy

I hope you got the point : I want to re-use the object copying behaviour, but hook-in my own operations. Is there a clean way to do this (without having to do for attr_name in dir(self): ...) ???

解决方案

You could just do:

def __copy__(self):
    clone = copy.deepcopy(self)
    clone._b = some_op(clone._b)
    return clone

This will work because deepcopy avoids recursion. From the python docs:

The deepcopy() function avoids these problems by: keeping a "memo" dictionary of objects already copied during the current copying pass; and letting user-defined classes override the copying operation or the set of components copied.

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