Python全栈之路----数据类型—字典

Posted 2021-02-02 沫小妤

字典：可变，一种key-value的数据类型

info = { ‘stu1101‘ : ‘TengLan Wu‘ , ‘stu1102‘ : ‘LongZe Luola‘ , ‘stu1103‘ : ‘ XiaoZe Maliya‘ }

     1.特点：key-value结构；key必须可hash（被hash值不变），且必须唯一、必须为不可变类型；无序的（因为无索引，通过key查询）；查找速度快

     2.基本操作：创建，添加，查找，修改，删除，清空

 1 >>> info = {
 2 ... ‘龙婷‘:[24,‘design‘,‘UI‘,2333],
 3 ...‘shanshan‘:[25,‘PR‘,‘wild model‘,13445222]
 4 ... }     #创建，‘：’前为key，后为value，value可为列表
 5 >>> info
 6 {‘龙婷‘: [24, ‘design‘, ‘UI‘, 2333], ‘shanshan‘: [25, ‘PR‘, ‘wild model‘, 13445222]}
 7 >>> info[‘龙婷‘] #查找时，字典名[key值]，若不存在，报错   
 8 [24, ‘design‘, ‘UI‘, 2333]
 9 >>> info[‘龙婷‘][1] = ‘设计部‘   #value为列表，修改和列表类似
10 >>> info
11 {‘龙婷‘: [24, ‘设计部‘, ‘UI‘, 2333], ‘shanshan‘: [25, ‘PR‘, ‘wild model‘, 13445222]}
12 >>> ‘shanshan‘ in info #判断‘shanshan‘是否在列表里面
13 True
14 >>> info.get(‘shanshan‘) #获取‘shanshan‘的字典值
15 [25, ‘PR‘, ‘wild model‘, 13445222]
16 >>> info[‘shanshan‘] #获取‘shanshan‘的字典值
17 [25, ‘PR‘, ‘wild model‘, 13445222]
18 >>> info[‘alex‘] #获取‘alex‘的字典值,如果不存在，就报错
19 Traceback (most recent call last):
20 File "<stdin>", line 1, in <module>
21 KeyError: ‘alex‘
22 >>> print(info.get(‘alex‘)) #获取‘alex‘的字典值，不存在返回为空
23 None
24 >>> info.pop(‘shanshan‘) #删除‘shanshan‘及其对应的value值，返回‘shanshan‘对应的value值
25 [25, ‘PR‘, ‘wild model‘, 13445222]
26 >>> info
27 {‘龙婷‘: [24, ‘design‘, ‘UI‘, 2333]}
28 >>> info.popitem() #随机删除，因为字典本身是无须的
29 (‘龙婷‘, [24, ‘design‘, ‘UI‘, 2333])
30 >>> info
31 {}
32 >>> info = {‘龙婷‘: [24, ‘design‘, ‘UI‘, 2333], ‘shanshan‘: [25, ‘PR‘, ‘wild model‘, 13445222]}
33 >>> info[‘name‘] = ‘alex‘ #添加 key 为‘name‘，对应value为‘alex‘
34 >>> info
35 {‘龙婷‘: [24, ‘design‘, ‘UI‘, 2333], ‘shanshan‘: [25, ‘PR‘, ‘wild model‘, 13445222], ‘name‘: ‘alex‘}
36 >>> del info[‘name‘] #删除‘name‘及其对应的value
37 >>> info
38 {‘龙婷‘: [24, ‘design‘, ‘UI‘, 2333], ‘shanshan‘: [25, ‘PR‘, ‘wild model‘, 13445222]}

    3.多级字典的嵌套

>>> catelog = { ‘A‘:{‘a‘:[‘1‘,‘5‘]},‘B‘:{‘b‘:[‘2‘,‘4‘]},‘C‘:{‘c‘:[‘3‘,‘6‘]}} #创建一个嵌套列表
>>> catelog[‘B‘][‘b‘][1] += ‘***‘ #修改
>>> catelog
{‘A‘: {‘a‘: [‘1‘, ‘5‘]}, ‘B‘: {‘b‘: [‘2‘, ‘4***‘]}, ‘C‘: {‘c‘: [‘3‘, ‘6‘]}}

     4.字典的用法：.keys() .values()  .items()  .update()  .setdefault()  .copy()->用法和列表完全一致

 1 >>> info = {‘alex‘:[24,‘IT‘],‘rain‘:[24,‘HR‘],‘jack‘:22}
 2 >>> info
 3 {‘alex‘: [24, ‘IT‘], ‘rain‘: [24, ‘HR‘], ‘jack‘: 22}
 4 >>> info.keys() #打印所有的key值
 5 dict_keys([‘alex‘, ‘rain‘, ‘jack‘])
 6 >>> info.values() #打印所有的value值
 7 dict_values([[24, ‘IT‘], [24, ‘HR‘], 22])
 8 >>> info.items() #将字典里的元素打印成小元组
 9 dict_items([(‘alex‘, [24, ‘IT‘]), (‘rain‘, [24, ‘HR‘]), (‘jack‘, 22)])
10 >>> info
11 {‘alex‘: [24, ‘IT‘], ‘rain‘: [24, ‘HR‘], ‘jack‘: 22}
12 >>> dic2 = {1:2,2:3,‘jack‘:[22,‘Jack Ma‘,‘Alibaba CEO‘]}
13 >>> info.update(dic2) #info和update合并,key值相同的被覆盖
14 >>> info
15 {‘alex‘: [24, ‘IT‘], ‘rain‘: [24, ‘HR‘], ‘jack‘: [22, ‘Jack Ma‘, ‘Alibaba CEO‘], 1: 2, 2: 3}
16 >>> info.setdefault(2,‘new 2‘)
17 3
18 >>> info
19 {‘alex‘: [24, ‘IT‘], ‘rain‘: [24, ‘HR‘], ‘jack‘: [22, ‘Jack Ma‘, ‘Alibaba CEO‘], 1: 2, 2: 3}
20 >>> info.setdefault(‘test‘,‘new 2‘) #有key就获取对应value值，没有就创建
21 ‘new 2‘
22 >>> info
23 {‘alex‘: [24, ‘IT‘], ‘rain‘: [24, ‘HR‘], ‘jack‘: [22, ‘Jack Ma‘, ‘Alibaba CEO‘], 1: 2, 2: 3, ‘test‘: ‘new 2‘}
24 >>> info.fromkeys([‘A‘,‘B‘,‘C‘]) #生成字典，给key批量赋值
25 {‘A‘: None, ‘B‘: None, ‘C‘: None}
26 >>> info.fromkeys([‘A‘,‘B‘,‘C‘],‘alex‘) #生成字典，给key批量赋值
27 {‘A‘: ‘alex‘, ‘B‘: ‘alex‘, ‘C‘: ‘alex‘}
28 >>> info
29 {‘alex‘: [24, ‘IT‘], ‘rain‘: [24, ‘HR‘], ‘jack‘: [22, ‘Jack Ma‘, ‘Alibaba CEO‘], 1: 2, 2: 3, ‘test‘: ‘new 2‘}

      5.字典循环

 

 

>>> for k in info:
... print(k) #打印key
...
alex
rain
jack
1
2
test

>>> for k in info:
... print(k,info[k]) #打印key和对应的value
...
alex [24, ‘IT‘]
rain [24, ‘HR‘]
jack [22, ‘Jack Ma‘, ‘Alibaba CEO‘]
1 2
2 3
test new 2

>>> for k,v in info.items():
... print(k,v) #打印key和value，但是比较低效（字典本身查询速度很快，此种方法将字典转化成了列表再循环，浪费时间），不建议使用
...
alex [24, ‘IT‘]
rain [24, ‘HR‘]
jack [22, ‘Jack Ma‘, ‘Alibaba CEO‘]
1 2
2 3
test new 2