如何改变python字典的__setattr__的行为？ [英] How to change the behavior of a python dictionary's __setattr__?

问题描述

在Python中，一切都有一个类。因此 dict 也有一个类。

所以理论上，我应该可以改变keyvalue赋值行为的实现。

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示例：

  d = dict（）
d ['first'] = 3＃内部d ['first']存储为6 [ie值* 2如果值为INT] 
 
打印d ['first']＃应打印6 
 
d ['second'] = 4 
 
 print d ['second']＃should print 8 
  

我注意到大多数对象具有列于 OBJECT .__ dict __ 或 vars（OBJECT）中的属性。但是，对于 dict 或列表，则不是这样。

如何通过覆盖 dict .__ setattr __（）方法获得所需的行为？

解决方案

这是 __ setitem __ 在这种情况下必须被覆盖 -
和它就像：

  class MyDict（dict）：
 def __setitem __（self，key，value）：
 dict .__ setitem __（self，key，2 * value）
  

示例：

 >>> m = MyDict（）
>>> m [0] = 5 
>>>> m 
 {0：10} 
  

__ setattr __ 控制对象属性本身（不是键/值对）的属性。

In Python, everything has a class. Therefore dict also has a class.

So, in theory, I should be able to change the implementation of the keyvalue assignment behavior.

Example:

d = dict()
d['first'] = 3    # Internally d['first'] is stored as 6 [i.e. value*2 if value is INT]

print d['first']  # should print 6

d['second'] = 4 

print d['second'] # should print 8

I noticed that most objects have attributes listed in OBJECT.__dict__ or vars(OBJECT). But this isn’t the case for dict or list.

How can I get the desired behavior by overriding dict.__setattr__() method?

解决方案

It is __setitem__ that have to be overriden in this case - and it is as simples as:

class MyDict(dict):
    def __setitem__(self, key, value):
         dict.__setitem__(self, key, 2 * value)

Example:

>>> m  = MyDict()
>>> m[0] = 5
>>> m
{0: 10}

__setattr__ controls how object attributes themselves (not key/value pairs) are attributed.

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