python 基础之第八天--字典相关

Posted 2020-10-02

zx

 

#####################创建字典######################################

 

In [11]: dict([(‘name‘,‘bob‘),(‘age‘,23),[‘qq‘,123456]])
Out[11]: {‘age‘: 23, ‘name‘: ‘bob‘, ‘qq‘: 123456}

In [12]: dict(((‘name‘,‘bob‘),(‘age‘,23),[‘qq‘,123456]))        ##dict函数
Out[12]: {‘age‘: 23, ‘name‘: ‘bob‘, ‘qq‘: 123456}

In [13]: aDict = {‘name‘:‘bob‘,‘age‘:23,‘qq‘:123456}       ##{}方式

In [14]: aDict
Out[14]: {‘age‘: 23, ‘name‘: ‘bob‘, ‘qq‘: 123456}

  In [20]: {}.fromkeys([‘bob‘,‘herry‘,‘jerry‘],7)      ##不同的key,相同的值，‘7’为值value
  Out[20]: {‘bob‘: 7, ‘herry‘: 7, ‘jerry‘: 7}

############关于循环字典取值###############

In [22]: for key in aDict:        ##默认只取key
   ....:     print key
   ....:     
qq
age
name

In [23]: for key in aDict:       ##key与value一起取
    print ‘%s-->%s‘ % (key,aDict[key])
   ....:     
qq-->123456
age-->23
name-->bob

#########特殊格式输出################
In [36]: aDict
Out[36]: {‘age‘: 23, ‘name‘: ‘bob‘, ‘qq‘: 123456}

In [37]: ‘%(name)s --> %(age)s‘ % aDict
Out[37]: ‘bob --> 23‘

##############删除（不常用），弹出与清空#############

#######aDict.pop##########
In [39]: aDict
Out[39]: {‘age‘: 23, ‘name‘: ‘bob‘, ‘qq‘: 123456}

In [41]: aDict.pop(‘age‘)  ###因为字典是无序的，所以需要指名pop哪个key
Out[41]: 23

In [42]: aDict
Out[42]: {‘name‘: ‘bob‘, ‘qq‘: 123456}

  In [43]: aDict.popitem()       ###popitem（）是随机弹的，几乎用不到，括号内不接受参数
  Out[43]: (‘qq‘, 123456)

  In [46]: uu = aDict.copy()    #复制字典

  In [47]: uu
  Out[47]: {‘name‘: ‘bob‘}

  In [48]: uu.clear()          ###清空字典

  In [49]: uu
  Out[49]: {}

##########字典的in 与not in #############

In [63]: aDict
Out[63]: {‘age‘: 23, ‘name‘: ‘herry‘}

In [64]: ‘age‘ in aDict          ###通过key查看是否在字典中，而不是value
Out[64]: True

#############字典长度##############

In [63]: aDict
Out[63]: {‘age‘: 23, ‘name‘: ‘herry‘}

In [66]: len(aDict)
Out[66]: 2

###########判断是否可以作为字典的key##########

In [67]: hash(‘naem‘)
Out[67]: -4166578487153698939

In [68]: hash(20)    
Out[68]: 20

In [69]: hash((10,30))
Out[69]: 3713074054223687331

In [70]: hash([10,30])
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-70-2766bfecf01d> in <module>()
----> 1 hash([10,30])

TypeError: unhashable type: ‘list‘

总结：通过hash函数，如果不报错，就是可以作为字典的key，我们会发现key都是不可变对象

#############字典的拷贝################

In [71]: aDict
Out[71]: {‘age‘: 23, ‘name‘: ‘herry‘}

In [72]: bDict = aDict.copy()

In [73]: bDict
Out[73]: {‘age‘: 23, ‘name‘: ‘herry‘}

In [74]: aDict
Out[74]: {‘age‘: 23, ‘name‘: ‘herry‘}

In [75]: id(aDict)
Out[75]: 45174528

In [76]: id(bDict)
Out[76]: 45199760

###########字典的get 用法（常用）############

In [71]: aDict
Out[71]: {‘age‘: 23, ‘name‘: ‘herry‘}

In [77]: aDict.get(‘age‘)    ###get key为‘age’ 的值23
Out[77]: 23

In [78]: aDict.get(‘qq‘)      ###get 不存在的key,返回值None

In [79]: print aDict.get(‘qq‘)
None

In [80]: aDict.get(‘qq‘,‘not found‘)      ########自定义，如果get 的key存在，则返回对应的值，不存在则返回我们定义的值，这边是‘not found’
Out[80]: ‘not found‘

In [81]: aDict.get(‘age‘,‘not found‘)  
Out[81]: 23

In [82]: aDict.get(‘name‘,‘not found‘)   
Out[82]: ‘herry‘

备注：

  In [83]: help(aDict.get)
  Help on built-in function get:

get(...)

      D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None.

In [90]: aDict.setdefault(‘age‘,33)      ####setdefault key，存在，则返回相对应的值，不存在则增加key-value
Out[90]: 20

In [91]: aDict
Out[91]: {‘age‘: 20, ‘name‘: ‘herry‘}

In [92]: aDict.setdefault(‘qq‘,333333)
Out[92]: 333333

In [93]: aDict
Out[93]: {‘age‘: 20, ‘name‘: ‘herry‘, ‘qq‘: 333333}

In [94]: help(aDict.setdefault)
Help on built-in function setdefault:

setdefault(...)
    D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D

##########################################################

In [100]: aDict
Out[100]: {‘age‘: 20, ‘name‘: ‘herry‘, ‘qq‘: 333333}

In [96]: aDict.keys()
Out[96]: [‘qq‘, ‘age‘, ‘name‘]

In [97]: aDict.values()     
Out[97]: [333333, 20, ‘herry‘]

In [98]: aDict.items()
Out[98]: [(‘qq‘, 333333), (‘age‘, 20), (‘name‘, ‘herry‘)]

实战案例：

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