python3.6之前 OrderedDict类（有序字典）

最新在学习一些知识用到有序字典，看到别人使用OrderedDict（）。但查阅资料发现，python3.6（包含）之后，所有的普通dict（）字典都变为有序的了，不再需要OrderedDict（）这个类了。如果你还是使用python2，或python3.5之前的版本，那可以继续浏览下，否者就没必须看了。

1.创建有序字典

所谓有序字典，就是插入键值对的顺序，是按照你插入的顺序来排列的。字典不会因为key或value的值，再自动排序！！

import collections

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

print(dic)

#输出：OrderedDict([('k3', 'v3'), ('k1', 'v1'), ('k2', 'v2')])

2.clear(清空有序字典)

import collections

dic = collections.OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
dic.clear()
print(dic)

#输出：OrderedDict()

3.copy(拷贝)

import collections

dic = collections.OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
new_dic = dic.copy()
print(new_dic)

#输出：OrderedDict([('k1', 'v1'), ('k2', 'v2')])

4.fromkeys(指定一个列表，把列表中的值作为字典的key,生成一个字典)

import collections

dic = collections.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)])

5.items(返回由“键值对组成元素“的列表)

import collections

dic = collections.OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
print(dic.items())

#输出：odict_items([('k1', 'v1'), ('k2', 'v2')])

6.keys(获取字典所有的key)

import collections

dic = collections.OrderedDict()
dic['k1'] = 'v1'
dic['k2'] = 'v2'
print(dic.keys())

# 输出：odict_keys(['k1', 'k2'])

7.move_to_end(指定一个key，把对应的key-value移到最后)

import collections
import collections

dic = collections.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')])

8.pop(获取指定key的value，并在字典中删除)

import collections
import collections

dic = collections.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')])

9.popitem(按照后进先出原则，删除最后加入的元素，返回key-value)

import collections

dic = collections.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')])

10.setdefault(获取指定key的value，如果key不存在，则创建)

import collections

dic = collections.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)])

11.values(获取字典所有的value，返回一个列表)

import collections

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

# 输出：odict_values(['v1', 'v2', 'v3'])

文章来源：
https://www.cnblogs.com/zhenwei66/p/6596248.html