OrderedDict类包含在collections模块中。
from collections import OrderedDict
基本方法
创建有序字典
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic['k3'] = 'v3'
print(dic)
"""
输出：OrderedDict([('k1', 'v1'), ('k2', 'v2'), ('k3', 'v3')])
"""
clear: 清空有序字典
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic.clear()
print(dic)
"""
输出：OrderedDict()
"""
copy: 复制有序字典
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
new_dic = dic.copy()
print(new_dic)
"""
输出：OrderedDict([('k1', 'v1'), ('k2', 'v2')])
"""
fromkeys: 列表转换
dic = OrderedDict()
name = ['tom','lucy','sam']
print(dic.fromkeys(name))
print(dic.fromkeys(name,20))
"""
输出：
OrderedDict([('tom', None), ('lucy', None), ('sam', None)])
OrderedDict([('tom', 20), ('lucy', 20), ('sam', 20)])
"""
items: 返回“键值对”列表
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
print(dic.items())
"""
输出：odict_items([('k1', 'v1'), ('k2', 'v2')])
"""
keys: 获取所有key
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
print(dic.keys())
"""
输出：odict_keys(['k1', 'k2'])
"""
move_to_end: 指定一个key，把对应的key-value移到最后
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic['k3'] = 'v3'
dic.move_to_end('k1')
print(dic)
"""
输出：OrderedDict([('k2', 'v2'), ('k3', 'v3'), ('k1', 'v1')])
"""
pop: 获取指定key的value，并在字典中删除
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic['k3'] = 'v3'
k = dic.pop('k2')
print(k,dic)
"""
输出：v2 OrderedDict([('k1', 'v1'), ('k3', 'v3')])
"""
popitem: 按照后进先出原则，删除最后加入的元素，返回key-value
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic['k3'] = 'v3'
print(dic.popitem(),dic)
print(dic.popitem(),dic)
"""
输出
('k3', 'v3') OrderedDict([('k1', 'v1'), ('k2', 'v2')])
('k2', 'v2') OrderedDict([('k1', 'v1')])
"""
setdefault: 获取指定key的value，如果key不存在，则创建
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic['k3'] = 'v3'
val = dic.setdefault('k5')
print(val,dic)
"""
输出：None OrderedDict([('k1', 'v1'), ('k2', 'v2'), ('k3', 'v3'), ('k5', None)])
"""
values: 获取字典所有的value，返回一个列表
dic = OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic['k3'] = 'v3'
print(dic.values())
"""
输出：odict_values(['v1', 'v2', 'v3'])
"""
注意
普通字典不考虑存储顺序，有序字典的顺序与加入键值的顺序有关。
但是调用keys方法时，返回值不考虑顺序。
dic['k2'] = 'v1'
dic['k1'] = 'v2'
dic2 = OrderedDict()
dic2['k1'] = 'v2'
dic2['k2'] = 'v1'
print(dic.keys() == dic2.keys())
print(dic == dic2)
dt = {'k2': 'v1', 'k1': 'v2'}
dt2 = {'k1': 'v2', 'k2': 'v1'}
print(dt.keys() == dt2.keys())
print(dt == dt2)
"""
输出:
True
False
True
True
"""
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