有序字典（orderedDict）

orderdDict是对字典类型的补充，他记住了字典元素添加的顺序

例：import collections

dic = collections.OrderedDict()
dic[‘k1‘] = ‘v1‘
dic[‘k2‘] = ‘v2‘
dic[‘k3‘] = ‘v3‘
print(dic)

得：

OrderedDict([(‘k1‘, ‘v1‘), (‘k2‘, ‘v2‘), (‘k3‘, ‘v3‘)])

把数据拿到最后def move_to_end(self, key, last=True):
        ‘‘‘Move an existing element to the end (or beginning if last==False).

        Raises KeyError if the element does not exist.
        When last=True, acts like a fast version of self[key]=self.pop(key).

        ‘‘‘
        link = self.__map[key]
        link_prev = link.prev
        link_next = link.next
        soft_link = link_next.prev
        link_prev.next = link_next
        link_next.prev = link_prev
        root = self.__root
        if last:
            last = root.prev
            link.prev = last
            link.next = root
            root.prev = soft_link
            last.next = link
        else:
            first = root.next
            link.prev = root
            link.next = first
            first.prev = soft_link
            root.next = link

例：import collections

dic = collections.OrderedDict()
dic[‘k1‘] = ‘v1‘
dic[‘k2‘] = ‘v2‘
dic[‘k3‘] = ‘v3‘
print(dic)
dic.move_to_end(‘k1‘)
print(dic)得：

OrderedDict([(‘k1‘, ‘v1‘), (‘k2‘, ‘v2‘), (‘k3‘, ‘v3‘)])
OrderedDict([(‘k2‘, ‘v2‘), (‘k3‘, ‘v3‘), (‘k1‘, ‘v1‘)])