14. Summary of methods in the Python dictionary

‘‘‘
1. Access, modify, delete the values in the dictionary:
‘‘‘

Dict={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print dict[' A '],dict[' d ']    #访问
dict[' B ']= ' abc '              #修改
Print Dict
#删除
Del dict[' C ']                #删除字典中的某个值
Print Dict
Dict.clear ()                 #清空字典
Print Dict
Del dict                     #删除字典
---------------------------------------------

11 44
{' A ': ' One ', ' C ': ' + ', ' B ': ' abc ', ' d ': ' 44 '}
{' A ': ' One ', ' B ': ' abc ', ' d ': ' 44 '}
{}

-----------------------------------------------------------------------------------

‘‘‘
2.len (): Calculates the total number of elements in the dictionary, that is, the total number of keys
‘‘‘
Dict={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print Len (dict)

---------------------------------------------

4

-----------------------------------------------------------------------------------

‘‘‘
3.fromkeys (seq,value): The function is used to create a new dictionary, which is the key for the dictionary of elements in the sequence SEQ, and value is the initial value corresponding to all the keys of the dictionary.
‘‘‘
Seq={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Dict=dict.fromkeys (seq)
Print Dict
Print Dict.fromkeys (seq,20)

---------------------------------------------

{' A ': none, ' C ': None, ' B ': none, ' d ': none}
{' A ': +, ' C ': +, ' B ': +, ' d ': 20}

-----------------------------------------------------------------------------------

‘‘‘
4.get (): Returns the value of the specified key, if the value is not in the dictionary, returns the default value
  SetDefault (): The function and the Get () method are similar, if the key does not exist in the dictionary, the key is added and the value is set to the default value.
‘‘‘

Seq={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print Seq.get (' a ')
Print Seq.get (' e ')
Print Seq.get (' e ', ' fuck ')
Print seq
Print Seq.setdefault (' e ', ' fuck ')
Print seq

---------------------------------------------

11
None
Fuck
{' A ': ' One ', ' C ': ' + ', ' B ': ' + ', ' d ': ' 44 '}
Fuck
{' A ': ' One ', ' C ': ' A ', ' B ': ' A ', ' e ': ' Fuck ', ' d ': ' 44 '}

-----------------------------------------------------------------------------------

‘‘‘
5.has_key (): Used to determine if the key exists in the dictionary, or False if the key returns true in the dictionary dict.
‘‘‘
Seq={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print Seq.has_key (' a ')
Print Seq.has_key (' m ')

---------------------------------------------

True
False

-----------------------------------------------------------------------------------

‘‘‘
6.items (): Returns an array of traversed (key, value) tuples in a list
‘‘‘
Seq={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print Seq.items ()
For k,v in Seq.items ():
    Print K,v

---------------------------------------------

[(' A ', ' one '), (' C ', ') ', (' B ', ') ', (' d ', ' 44 ')]
A 11
C 33
b 22
D 44

-----------------------------------------------------------------------------------

‘‘‘
7.keys (): Returns all keys in a dictionary in a list
‘‘‘
Seq={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print Seq.keys ()

---------------------------------------------

[' A ', ' C ', ' B ', ' d ']

-----------------------------------------------------------------------------------

‘‘‘
8.dict.update (DICT2): Update key values in Dict2 to Dict
‘‘‘
Dict={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
dict1={' AAA ': ' 111 ', ' BBB ': ' 222 '}
Dict.update (Dict1)
Print Dict

---------------------------------------------

{' A ': ' One ', ' C ': ' + ', ' B ': ' + ', ' aaa ': ' 111 ', ' d ': ' + ', ' BBB ': ' 222 '}

-----------------------------------------------------------------------------------

‘‘‘
9.values (): Returns all values in the dictionary as a list
‘‘‘
Dict={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print dict.values ()

---------------------------------------------

[' 11 ', ' 33 ', ' 22 ', ' 44 ']

-----------------------------------------------------------------------------------

‘‘‘
10.pop (Key[,default]): Removes the value of the dictionary given key key, and the return value is the deleted value. The key value must be given. Otherwise, the default value is returned.
‘‘‘
Dict={' a ': ' One ', ' B ': ' A ', ' C ': ' + ', ' d ': ' 44 '}
Print Dict.pop (' a ')
Print Dict.pop (' e ', ' Notall ')

---------------------------------------------

11
Notall

-----------------------------------------------------------------------------------

14. Summary of methods in the Python dictionary