"Python" dictionary ~ in-depth article

Definition of a dictionary

A dictionary is a series of key-value pairs, which are represented by a series of key-value pairs placed in {}

info = {'first_name':'yueshang','last_name  ':'QIN',' age':'  ' city':'KunMing'}

Dictionary increment, delete, change, check

Add new elements

Specifies the dictionary name, the key enclosed in square brackets, and the associated value

info['sex']='man'

modifying elements

Specifies the dictionary name, the key enclosed in square brackets, and the new value associated with the key

info['sex']='Woman'

Inquire

Specify the dictionary name and the key that is enclosed in parentheses

Print (info['sex')

In practice, it is possible that a dictionary contains thousands of key-value pairs, so a traversal is required to fully access the key value

Traverse all key values to items ()

 for inch Info.items ():     Print ("\nkey:" + key)     Print ("\nvalue:" + value)

Traverse all keys

 for inch Info.keys ():     Print (key)

Traverse All Values

 for inch info.values ():     Print (value)

Note: When traversing, if you need to sort the traversed keys, then use sorted (). Values are the same

Use of the Set () method: The Set () method can repeat the element

Set () case

Letter = {'1':'A','2':'B','3':'C','4':'A'} forIinchSet (Letter.values ()):Print(i)

Print Result: C A B

Delete

Use the DEL statement to delete the corresponding key-value pair

del info['sex']

Deleted key-value pairs disappear forever.

Nesting

Sometimes you need to store a series of dictionaries in a list, or you can store a list in a dictionary, which is called nesting.

To store a dictionary in a list

Now there are three athletes in the country, with a list to store information about the athletes in each country.

America_player = {'name':'Tom',' Age': 24}china_player= {'name':'Zhangsan',' Age': 27}japan_player= {'name':'Jinshang',' Age': 25}players=[America_player,china_player,japan_player] forPalyerinchPlayers:Print(Palyer)

Nesting lists in a dictionary

Now there are 2 people, each with their own favorite fruit list, we need to store all this information, then use a dictionary, where elements are a list.

Favorite_fruits = {    'Zhangsan':['Apple','Pear'],    'Lisi':['Orange','Apple']} forName,fruitsinchFavorite_fruits.items ():Print("\ n"+name.title () +"' s favorite fruits is:")     forFruitinchFruits:Print("\ n"+fruit.title ())

Nesting dictionaries in a dictionary

Here are 2 Web sites, each corresponding to a different user name, the dictionary stored in a dictionary to meet this requirement

Users = {    'website1':{        'name':'Zhangsan',        'Password':'123'    },    'Website2': {        'name':'Lisi',        'Password':'456'    }} forWebsite,logininfoinchUsers.items ():Print("\nwebsite:"+Website)Print("\tusername:"+logininfo['name'])    Print("\tpassword:"+ logininfo['Password'])

"Python" dictionary ~ in-depth article