Python ordered dictionary usage

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foreword

Record new knowledge encountered in work, as an essay

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1. Ordered dictionary

Because the dictionary itself is a hash table, it is unordered. And sometimes specific scenarios require ordered dictionaries.
An ordered dictionary is similar to a normal dictionary, except that it can record the order in which elements are inserted into it, while a normal dictionary will iterate in any order.

2. Use steps

1. Import library

import collections

2. Instantiate an ordered dictionary object

dic = collections.OrderedDict()

3. Dynamically add and output in the order of addition

dic = collections.OrderedDict()
dic['a'] = 'A'
dic['b'] = 'B'
dic['c'] = 'C'
dic['d'] = 'D'
print(dic)
#输出内容：OrderedDict([('a', 'A'), ('b', 'B'), ('c', 'C'), ('d', 'D')])

4. Precautions

Ordered dictionaries are output in insertion order

import collections
dic = {
    
    'a':'A','b':'B','c':'C','d':'D'}
dic = collections.OrderedDict()
print(d2)
输出结果为空

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Summarize

Using an ordered dictionary needs to be instantiated in advance, and then inserted in the desired order. OrderedDict can implement a FIFO (first in, first out) dict. When the capacity exceeds the limit, delete the earliest added Key first.