用OrderedDict替换对象的默认__dict__

Question

我的代码中有两个类.first是second继承的父.

class first(object):
    def __init(self,**kwargs):  
        pass

    def __setattr__(self,name,value):
        self.__dict__[name] = value

class second(first):
    def do_something(self):
        self.a = 1
        self.b = 2
        self.c = 3

当我打印第二类(例如second.__dict__)时,我得到无序字典.这很明显.我想更改此行为以使用OrderedDict该类获取有序字典,但它不起作用.我正在first通过以下方式更改实现:

class first(OrderedDict):   
    def __init__(self,**kwargs):  
        super(first,self).__init__(**kwargs)  
    def __setattr__(self,name_value):  
        super(first,self).__setattr__(name_value)  

我想second用__dict__或打印__repr__,但我得到了无序字典.我应该改变什么？

Answer 1

您可以简单地将所有属性访问重定向到OrderedDict:

class first(object):
    def __init__(self, *args, **kwargs):  
        self._attrs = OrderedDict(*args, **kwargs)

    def __getattr__(self, name):
        try:
            return self._attrs[name]
        except KeyError:
            raise AttributeError(name)

    def __setattr__(self, name, value):
        if name == '_attrs':
            return super(first, self).__setattr__(name, value)
        self._attrs[name] = value

演示:

>>> from collections import OrderedDict
>>> class first(object):
...     def __init__(self, *args, **kwargs):  
...         self._attrs = OrderedDict(*args, **kwargs)
...     def __getattr__(self, name):
...         try:
...             return self._attrs[name]
...         except KeyError:
...             raise AttributeError(name)
...     def __setattr__(self, name, value):
...         if name == '_attrs':
...             return super(first, self).__setattr__(name, value)
...         self._attrs[name] = value
... 
>>> class second(first):
...     def do_something(self):
...         self.a = 1
...         self.b = 2
...         self.c = 3
... 
>>> s = second()
>>> s.do_something()
>>> s._attrs
OrderedDict([('a', 1), ('b', 2), ('c', 3)])

您不能__dict__用OrderedDict实例替换该属性,因为Python通过使用具体的类API来访问C中的字典内部优化实例属性访问,OrderedDict.__setitem__完全绕过钩子(参见问题#1475692).

Answer 2

我认为这个线程中的解决方案过于关注使用，OrderedDict就好像它是必需的一样。该类已经有一个内置__dict__方法，唯一的问题是键的排序。以下是我如何(key, value)按照输入顺序从班级中检索对：

class MyClass:

    def __init__(self, arg1, arg2, arg3):
        self._keys = []
        self.arg1 = arg1
        self.arg2 = arg2
        self.arg3 = arg3

    def __setattr__(self, key, value):
        # store new attribute (key, value) pairs in builtin __dict__
        self.__dict__[key] = value
        # store the keys in self._keys in the order that they are initialized
        # do not store '_keys' itelf and don't enter any key more than once 
        if key not in ['_keys'] + self._keys:
            self._keys.append(key)

    def items(self):
        # retrieve (key, value) pairs in the order they were initialized using _keys
        return [(k, self.__dict__[k]) for k in self._keys]

>>> x = MyClass('apple', 'orange', 'banana')
>>> print x.items()
[('arg1', 'apple'), ('arg2', 'orange'), ('arg3', 'banana')]
>>> x.arg1 = 'pear'
>>> print x.items()
[('arg1', 'pear'), ('arg2', 'orange'), ('arg3', 'banana')]

我使用一个类来存储大约 70 个变量，用于配置和运行一个更大的程序。我保存了初始对的文本副本(key, value)，可用于初始化类的新实例。我还在(key, value)运行程序后保存了这些对的文本副本，因为其中一些对在程序运行期间被设置或更改。(key, value)当我想浏览结果时，按顺序排列这些对可以提高文本文件的可读性。