How to keep a dictionary in order in python (code)
Oct 11, 2018 pm 02:24 PMThe content of this article is about how Python keeps the dictionary in order (code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
1. Requirements
We want to create a dictionary, and at the same time, when iterating or serializing the dictionary, we can also control the order of the elements in it.2. Solution
To control the order of elements in the dictionary, you can use the OrderedDict class in the collections module. When iterating over a dictionary, it does so strictly in the order in which the elements were originally added.
from collections import OrderedDict d=OrderedDict() d['a']=1 d['b']=2 d['c']=3 d['d']=4 #根据插入删除输出 for key in d: print(key,d[key])
Result:
a 1 b 2 c 3 d 4
OrderedDict is particularly useful when you want to build a mapping structure that can later be serialized or encoded into another format. For example: If you want to accurately control the order of each field when encoding JSON, then you only need to construct the data in OrderedDict first:
from collections import OrderedDict import json d=OrderedDict() d['a']=1 d['b']=2 d['c']=3 d['d']=4 j=json.dumps(d) print(j)
Result:
{"a": 1, "b": 2, "c": 3, "d": 4}
Please note: OrderedDict is 2 times the size of an ordinary dictionary. This is due to the additional linked list it creates. Therefore, if you plan to build a data structure that involves a large number of OrderedDict instances (for example, reading 100,000 rows from a CSV file into an OrderedDict list), you will need to perform a requirements analysis of the application to determine the benefits of using OrderedDict. Can the disadvantages of additional memory overhead be overcome?
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