How to use the python3 OrderedDict class (ordered dictionary)

Create an ordered dictionary

import collections
dic = collections.OrderedDict()
dic['k1'] = 'v1'dic['k2'] = 'v2'dic['k3'] = 'v3'print(dic)#输出：OrderedDict([('k1', 'v1'), ('k2', 'v2'), ('k3', 'v3')])

clear(clear the ordered dictionary)

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

copy(copy)

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')])

fromkeys(specify a list and copy the values ​​in the list As the key of the dictionary, generate a dictionary)

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)])

items(return a list of "key-value pairs")

import collections
dic = collections.OrderedDict()
dic['k1'] = 'v1'dic['k2'] = 'v2'print(dic.items())#输出：odict_items([('k1', 'v1'), ('k2', 'v2')])

keys(get all the keys of the dictionary)

import collections
dic = collections.OrderedDict()
dic['k1'] = 'v1'dic['k2'] = 'v2'print(dic.keys())# 输出：odict_keys(['k1', 'k2'])

move_to_end(Specify a key and move the corresponding key-value to the end)

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')])

pop(Get the value of the specified key and delete it in the dictionary)

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')])

popitem(Follow the last step) First out principle, delete the last element added and return 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')])

setdefault(get the value of the specified key, if the key does not exist, create it)

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)])

values(get all the dictionary value, returns a list)

import collections
dic = collections.OrderedDict()
dic['k1'] = 'v1'dic['k2'] = 'v2'dic['k3'] = 'v3'print(dic.values())# 输出：odict_values(['v1', 'v2', 'v3'])

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