如何“完美”覆盖一个dict？ [英] How to "perfectly" override a dict?
问题描述
尽可能使我们做出完美的的子类。最终目标是拥有一个简单的 dict ，其中的键是小写的。
How can I make as "perfect" a subclass of dict as possible? The end goal is to have a simple dict in which the keys are lowercase.
看起来应该是一些很小的原语集可以重写这项工作，但是我所有的研究和尝试都使得它似乎并非如此：
It would seem that should be some tiny set of primitives I can override to make this work, but all my research and attempts have made it seem like this isn't the case:
-
如果我覆盖
__ getitem __/__ setitem __，然后获取/设置不工作。
我如何让他们工作？当然，我不需要单独实现它们。
If I override
__getitem__/__setitem__, thenget/setdon't work. How do I make them work? Surely I don't need to implement them individually?
我防止酸洗工作，我需要实现 __ setstate __ etc？
Am I preventing pickling from working, and do I need to implement __setstate__ etc?
Do I need repr, update and __init__?
我应该只是使用mutablemapping （似乎不应该使用 UserDict
或 DictMixin ）？如果是这样，怎么办？文件并不完全启发。
Should I just use mutablemapping (it seems one shouldn't use UserDict
or DictMixin)? If so, how? The docs aren't exactly enlightening.
这是我第一次去， get （）至少不起作用，毫无疑问有很多微妙的问题：
Here is my first go at it, get() doesn't work at least, and no doubt there are many minor subtle problems:
class arbitrary_dict(dict):
"""A dictionary that applies an arbitrary key-altering function
before accessing the keys."""
def __keytransform__(self, key):
return key
# Overridden methods. List from
# http://stackoverflow.com/questions/2390827/how-to-properly-subclass-dict
def __init__(self, *args, **kwargs):
self.update(*args, **kwargs)
# Note: I'm using dict directly, since super(dict, self) doesn't work.
# I'm not sure why, perhaps dict is not a new-style class.
def __getitem__(self, key):
return dict.__getitem__(self, self.__keytransform__(key))
def __setitem__(self, key, value):
return dict.__setitem__(self, self.__keytransform__(key), value)
def __delitem__(self, key):
return dict.__delitem__(self, self.__keytransform__(key))
def __contains__(self, key):
return dict.__contains__(self, self.__keytransform__(key))
class lcdict(arbitrary_dict):
def __keytransform__(self, key):
return str(key).lower()
推荐答案
您可以使用 ABC s
（抽象基类）从集合模块。它甚至告诉你
如果你错过了一个方法，所以下面是关闭ABC的最小版本。
You can write an object that behaves like a dict quite easily with ABCs (Abstract Base Classes) from the collections module. It even tells you if you missed a method, so below is the minimal version that shuts the ABC up.
import collections
class TransformedDict(collections.MutableMapping):
"""A dictionary that applies an arbitrary key-altering
function before accessing the keys"""
def __init__(self, *args, **kwargs):
self.store = dict()
self.update(dict(*args, **kwargs)) # use the free update to set keys
def __getitem__(self, key):
return self.store[self.__keytransform__(key)]
def __setitem__(self, key, value):
self.store[self.__keytransform__(key)] = value
def __delitem__(self, key):
del self.store[self.__keytransform__(key)]
def __iter__(self):
return iter(self.store)
def __len__(self):
return len(self.store)
def __keytransform__(self, key):
return key
您可以从ABC获得一些免费方法：
You get a few free methods from the ABC:
class MyTransformedDict(TransformedDict):
def __keytransform__(self, key):
return key.lower()
s = MyTransformedDict([('Test', 'test')])
assert s.get('TEST') is s['test'] # free get
assert 'TeSt' in s # free __contains__
# free setdefault, __eq__, and so on
import pickle
assert pickle.loads(pickle.dumps(s)) == s
# works too since we just use a normal dict
我不会直接子类 dict （或其他内置函数）。它通常没有任何意义，因为您实际想要做的是实现dict的界面。这正是ABCs所用的。
I wouldn't subclass dict (or other builtins) directly. It often makes no sense, because what you actually want to do is implement the interface of a dict. And that is exactly what ABCs are for.
这篇关于如何“完美”覆盖一个dict？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
