Python Learning notes--dictionaries

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