Explanation of python Dictionary and List Nesting Usage
- 2021-11-13 08:23:42
- OfStack
The use of dictionaries and lists in python should be the most commonly used in data processing, and these two proficiency can basically cope with most scenes. However, the basic tutorials on the Internet only tell you what lists, dictionaries are and how to use them, and seldom do combination instructions.
Just when collecting prometheus monitoring interface and doing data processing, I used a lot of combination scenes, and listed a few to share.
List (List)
Sequence is the most basic data structure in Python. Each element in the sequence is assigned a number-its position, or index, the first index is 0, the second index is 1, and so on.
List is the most commonly used Python data type and can appear as a comma-separated value within 1 square bracket.
The data items of the list do not need to have the same type
The characteristics are: repeatable and different types
Common ways
To create a list, just enclose different data items separated by commas in square brackets. As shown below:
list1 = ['apple', 'banana', 2008, 2021]
list2 = [1, 2, 3, 4, 5 ]
list3 = ["a", "b", "c", "d"]
### Toward list Add elements to
list1.append(3) ## ['apple', 'banana', 2008, 2021, 3]
### Use extend Used to connect list
list1.extend([7, 8]) ##['apple', 'banana', 2008, 2021, 3, 7, 8]
### insert Insert a single element into the list Medium
list3.insert(2, 'q') ##['a', 'b', 'q', 'c', 'd']
### Gets the length of the list
print(len(list1)) ## 5
### Traversal list
for name in list1:
print(name)extend (extension) and append (append) look similar, but in fact they are completely different.
extend accepts a parameter, which is always an list, and adds each element of this list to the original list. append accepts one parameter, which can be of any data type, and is simply appended to the tail of list.
Dictionary (dictionary)
Dictionary is another variable container model, and can store objects of any type.
The key (key) must be 1-only and can be used as a number, string, or tuple, but not a list The same key appears twice, and the last one will update the value of the previous one.Common ways
Each key value of the dictionary
key=>value
Contrast colons
:
Split, with commas between each key-value pair
,
Split, the whole dictionary is included in curly braces
{}
The format is as follows:
>>> dict = {'a': 1, 'b': 2, 'b': '3'}
>>> print(dict)
{'a': 1, 'b': '3'}
### Access the values in the dictionary
>>> print(dict['b'])
3
### Update and add dictionaries
>>> dict['a'] = 8
>>> dict['c'] = 'cc'
>>> print(dict['a'])
8
>>> print(dict['c'])
cc
### Delete dictionary elements
>>> del dict['a']
>>> print(dict)
{'b': '3', 'c': 'cc'}
>>> dict.clear() # Empty all entries in the dictionary
>>> del dict # Delete dictionary
Combined use
Lists can also be nested in lists, and dictionaries can be nested in lists
Dictionaries can be nested in dictionaries, and lists can also be nested in dictionaries
This is very flexible.
List nested list
This is not used much, and it is relatively simple. Look at the example directly:
### Printout character 5
l = [[1,2],[3,4],[[5,6],[7,8]]]
>>> print(l[2][0][0])
5
### Convert a nested list to a non-nested list
>>> a = [[1,2,3],[4,5,6],[7],[8,9]]
>>> for i in a:
... t.extend(i)
...
>>> print(t)
[1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 7, 8, 9]
List nested dictionary
Nesting dictionaries in the list should be the most commonly used way. Give an example directly:
li = [{'a': 1}, {'b': 2}, {'c': 3}]
###(1) Loop to get every key-value pair in the dictionary :
>>> for i in range(len(li)):
... for k, v in li[i].items():
... print(k, v)
...
a 1
b 2
c 3
###(2) Get each key-value pair in the dictionary ( Tuple data type ):
>>> for i in range(len(li)):
... for j in li[i].items():
... print(j)
...
('a', 1)
('b', 2)
('c', 3)
### You can see the 2 The obtained key-value pair is Tuple data type.
Dictionary nested dictionary
Dictionary nested dictionary: String as key, dictionary as value:
>>> s={'a':{0:'no',1:{'f':{0: 'no', 1: 'maybe'}}},'b':{}} # Construction dictionary
>>> s['a'][0] # Value
'no'
>>> s['a'][1]
{'f': {0: 'no', 1: 'maybe'}}
>>> s['a'][1]['f'][1]
'maybe'
### Dictionary nested dictionary
dict = {
'192.168.1.1':{'cpu':'0.23',' Memory ':'16',' Hard disk ':'500'},
'192.168.1.2':{'cpu':'3.22',' Memory ':'64',' Hard disk ':'700'},
'192.168.1.3':{'cpu':'1.99',' Memory ':'32',' Hard disk ':'800'},
}
### for Traversal
>>> for k,v in dict.items():
... print('\n',k,end=': ')
... for x,y in v.items():
... print(x,y,end=' ')
...
192.168.1.1: cpu 0.23 Memory 16 Hard disk 500
192.168.1.2: cpu 3.22 Memory 64 Hard disk 700
192.168.1.3: cpu 1.99 Memory 32 Hard disk 800
Dictionary nested list
So how do you nest lists in a dictionary?
Dictionary nested list: string as key, list as value.
### Dictionary nested list
dict = {
' Fruit ':[' Apple ',' Banana ',' Orange '],
' Animals ':[' Lion ',' Tiger ',' Elephant '],
' Language ':[' Chinese ',' English ',' Japanese '],
}
### Access the values in the dictionary
>>> print(dict[' Fruit '])
[' Apple ', ' Banana ', ' Orange ']
### Access the value in the list
>>> print(dict[' Language '][1])
English
### Cyclic printout to see the effect
>>> for k, v in dict.items():
... print('\n', k, end=':')
... for x in v:
... print(x,end=' ')
...
Fruit : Apple Banana Orange
Animals : Lion Tiger Elephant
Language : Chinese English Japanese
When is nesting used
For example, when you want to store the scores of the top 100 students in grade, because the students are ranked by their scores, the list is an ordered data type, and the dictionary is an unordered data type, so all the data will be stored in the list outside.
For students' grades in various subjects, what they value is not order, but the correspondence between subjects and grades 11, which is the most important thing. In other words, when I want to get the Chinese scores of the 10th classmate, I can directly get the index corresponding to the list and the key corresponding to the dictionary, so that I can get the corresponding value.
As for sorting usage in nesting
References
List: https://www.runoob.com/python/python-lists.html
Dictionary: https://www.runoob.com/python/python-dictionary.html
Nested dictionaries: https://www.pythonf.cn/read/100118 # 1.2 Nested list of dictionaries