Python Learning notes--dictionaries

Source: Internet
Author: User

dictionary (dict): The combination of unordered data that exists as a key-value pair is a dictionary, why do you say that, we all know that we have learned that the series such as lists, sets, etc. are only a single data can be stored, if you want to store the relevant data is more troublesome, For example, we want a person's name and his gender corresponding to the storage, this time using the list and so on more trouble, then we draw the concept of the dictionary,

definition : A combination of unordered data that exists as a key-value pair is a dictionary,

features : The dictionary stores data is stored in key-value pairs, so-called key-value pairs (key&values) is a key corresponding to a value, then the associated data can be stored

format : dicts = {' A ': ' A '} #注意此时数据是以冒号连接的, the identity symbol is curly brace {}.

simple creation of dictionaries :

1. Create an empty dictionary

Dicts = {} or vardict = Dict ()

2. Create a dictionary with multiple data

2.1 dicts = {' A ': ' A ', ' B ': ' B ', ' C ': ' C '}

2.2 Dicts = Dict ({' A ': ' A ', ' B ': ' B ', ' C ': ' C '})

2.3 dicts = dict (a = ' a ', B = ' B ', c = ' C ')

2.4 lists = [

[' A ', ' a '],

[' B ', ' B ']

]

res = dict (lists)-to-print (res) #注意, only this structure can be converted to a list-to-dictionary

2.5 keys = [' A ', ' B ', ' C ']

values = [' A ', ' B ', ' C ']

res = dict (Zip (keys,values))

Print (res) #这种格式也可以得到字典

Basic operation of the dictionary:

Create a dictionary using: vardict = {' A ': ' A ', ' B ': ' B ', ' C ': ' C ', ' d ': ' d ', ' e ': ' E ', ' F ': ' F '}

1. Accessing values in the dictionary

Print (vardict [' B ']) #访问时书写字典的key, you can get the value of the dictionary

2. Modify the Dictionary

Vardict[' e '] = EE #此时操作就会将原有的e对应的E改成EE

Vardict[' g '] = g #在字典中增加一个键值对 g->g

3. Delete a dictionary

Del vardict [' C '] #次操作删除了原有字典c所对应的键值对

4. Member Detection

Print (' C ' in vardict) #检测成员c是否在字典vardict中 so that only the key can be detected

The traversal operation of the dictionary

Method One: #先遍历键, in the value

For I in Vardict:

Print (i, vardict [i])

Method Two: Simultaneously traverse the key and the value

For x, y in Vardict.items ():

Print (x, y)

Dictionary derivation type

Create the dictionary you use

Vardict = {' A ': ' A ', ' B ': ' B ', ' C ': ' C '}

Vardict2 = {' name ': ' Old king ', ' age ': ' + ', ' sex ': ' Man '}

1. General Deduction Formula

Print ({' * ' + k + ' * ' : ' * ' + k + ' * ' for k,v in Vardict.items ()})

2. Expressions with judging criteria

Print ( k:v for k,v in Vardict2.items () If Len (2) = = 2})

3. Multi-loop Dictionary expressions

Print ({a+x:b+y for a, b in Vardict.items () for x, y in Vardict2.items ()})

Related functions of the dictionary 

Create the dictionary you use

Vardict = {' A ': ' A ', ' B ': ' B ', ' C ': ' C '}

1.clear () Empty dictionary

Vardict.clear () #此操作会清空字典的所有内容, please note

2. Copy () Duplicate dictionary

New_vardict = Vardict.copy ()

3. Fromkeys () use a sequence (as a dictionary key) and a specified value to make a dictionary

Lists = [1,2,3,4,5,6]

New_vardict = Dict.fromkeys (lists, ' Python ') or new_vardict = '. Fromkeys (lists, ' Python ')

4.get () Gets the value of the specified key in the dictionary

Vardict.get (' A ', ' return value ') #等价于 var[' a '] #注意get有返回值, the query does not return the returned value after

5.setdefault () Add an element to the dictionary (nonexistent key added, existing key is not moved)

Vardict.setdefult (' F ', ' F ')

6.update () modifying elements in a dictionary

Vardict.update (a = ' a ') or var.update ({' A ': ' A '})

7.pop () removes the specified element from the dictionary

Vardict.pop (' B ')

8.popitem () randomly deletes an element from the dictionary

Vardict.popitem ()

9.keys () Gets a container of all the keys in the dictionary

Print (Var.keys ())

10.values () Gets a container of all the keys in the dictionary

Print (Var.values ())

11.items () Gets a container of all the keys and values in the dictionary

Print (Vardict.items ())

#注: If you have errors or questions, email: [Email protected]

Python Learning notes--dictionaries

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.