具有列表功能的有序字典实现 ListOrderedDict

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title: 具有列表功能的有序字典实现 ListOrderedDict mathjax: false tags: [Python] categories: [Python]

字典和列表都是python中常用的数据结构，各自有各自的优点，但有没有可以结合他们优点的数据结构呢，本文初步实现了具有列表功能的有序字典， 取名 ListOrderedDict。

背景

在python编程中，遇到了字典需要有序的情况，可以使用 collections 库中的 OrderedDict，在保持字典功能的同时使得其元素保持输入顺序；

但在此基础上又需要他拥有列表的性质：

• 按序号索引
• 切片提取数据
• append 和 pop 操作

这就得自己开发了

ListOrderedDict 实现

class ListOrderedDict(OrderedDict):
    def __getitem__(self, key):
        if is_integer(key):
            key = list(self.keys())[key]
        elif isinstance(key, slice):
            slicedkeys = list(self.keys())[key]
            lod_obj = type(self)()
            for slicedkey in slicedkeys:
                lod_obj[slicedkey] = self[slicedkey]
            return lod_obj
        return super().__getitem__(key)

    def append(self, key, value):
        if is_integer(key):
            raise RuntimeError(f" integer key is not allowed in ListOrderedDict {key}.")
        assert key not in self, f"cannot add existed key. {key}"
        self[key] = value
    
    def __setitem__(self, key, value):
        'od.__setitem__(i, y) <==> od[i]=y'
        # Setting a new item creates a new link at the end of the linked list,
        # and the inherited dictionary is updated with the new key/value pair.
        if is_integer(key):
            raise RuntimeError(f" integer key is not allowed in ListOrderedDict {key}.")
        else:
            return super().__setitem__(key, value)

    def __delitem__(self, key):
        'od.__delitem__(y) <==> del od[y]'
        # Deleting an existing item uses self.__map to find the link which gets
        # removed by updating the links in the predecessor and successor nodes.
        if is_integer(key):
            key = list(self.keys())[key]

        return super().__delitem__(key)

    def move_to_end(self, key, last=True):
        '''Move an existing element to the end (or beginning if last is false).

        Raise KeyError if the element does not exist.
        '''
        if is_integer(key):
            key = list(self.keys())[key]

        return super().move_to_end(key, last)

    def __repr__(self):
        'od.__repr__() <==> repr(od)'
        if not self:
            return '%s()' % (self.__class__.__name__,)
        return '%s(%r)' % (self.__class__.__name__, list(self.items()))

    def pop(self, key=-1):
        '''od.pop(k[,d]) -> v, remove specified key and return the corresponding
        value.  If key is not found, d is returned if given, otherwise KeyError
        is raised.
        '''
        if is_integer(key):
            if len(list(self.keys())) == 0:
                print(f"pop a None from an empty ListOrderedDict.")
                return None
            key = list(self.keys())[key]
        return super().pop(key)

    def setdefault(self, key, default=None):
        '''Insert key with a value of default if key is not in the dictionary.

        Return the value for key if key is in the dictionary, else default.
        '''
        if is_integer(key):
            key = list(self.keys())[key]
        return super().setdefault(key, default)
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初步实现

• 按整数下标提取元素
• 切片
• append
• pop
• 其他有序字典操作

使用

功能集成在了我的常用库 mtutils 中，可以pip直接安装

pip install mtutils
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之后直接引用

from mtutils import ListOrderedDict
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注意

• 为了保持几种特性，牺牲了整数作为字典 key 的能力
• 有问题欢迎随时交流