dict的特性和基本语法—

特性

key:value结构，字典中的每一个元素，都是键值对
key必须可被hash，且必须为不可变数据类型，必须唯一
可存放任意多个值，可修改，可以不唯一
无序
查找速度快，因为hash可以把key变成数字，数字则可通过二分法快速查找，提高查找效率

基本语法

clear：清空字典

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info)    # =>{'stu1': 'LiLei', 'stu2': 'HanMeiMei', 'stu3': 'XiaoMing'}

Info.clear()

print(Info)    # =>{}

copy：复制字典

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

Info_new = Info.copy()

print(Info_new)   # =>{'stu1': 'LiLei', 'stu2': 'HanMeiMei', 'stu3': 'XiaoMing'}

fromkeys：返回一个新的字典，key值可迭代，但所有的value都是相等的

Info = {}

Info_new = Info.fromkeys([1,2,3],'Hi')

print(Info_new)   # =>{1: 'Hi', 2: 'Hi', 3: 'Hi'}

get：通过key获取对应的value，如果字典中key存在，则返回对应的value，如果不存在，返回None

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info.get('stu2'))# =>HanMeiMei

print(Info.get('stu4'))# =>None

items：获取所有的key-value，以列表方式呈现

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info.items())# =>dict_items([('stu1', 'LiLei'), ('stu2', 'HanMeiMei'), ('stu3', 'XiaoMing')])

keys：获取所有的key

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info.keys()) # =>dict_keys(['stu1', 'stu2', 'stu3'])

values：获取所有的values

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info.values()) # =>dict_values(['LiLei', 'HanMeiMei', 'XiaoMing'])

pop：pop(self,k,d=None)删除指定的key，如果key存在，则返回对应的value，如果key不存在，则返回指定的d，如果d未指定，则报错

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info.pop('stu1'))# =>LiLei

print(Info.pop('stu4',0))# =>0

print(Info.pop('stu4'))# =>报错

popitem：删除字典中的一对key-value，无序的，当字典为空时，报错

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info.popitem())# =>('stu3', 'XiaoMing')

print(Info.popitem())# =>('stu2', 'HanMeiMei')

print(Info.popitem())# =>('stu1', 'LiLei')

print(Info.popitem())# =>报错

setdefault：setdefault(self,k,d=None)如果key存在，则返回对应的value，如果key不存在，则将该key-value添加进字典，并返回该value（即指定的d），若d未指定，则为None

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

print(Info.setdefault('stu3','Jack'))# =>XiaoMing

print(Info)# =>{'stu1': 'LiLei', 'stu2': 'HanMeiMei', 'stu3': 'XiaoMing'}

print(Info.setdefault('stu4','Jack'))# =>Jack

print(Info)# =>{'stu1': 'LiLei', 'stu2': 'HanMeiMei', 'stu3': 'XiaoMing', 'stu4': 'Jack'}

update：更新字典，若key不重复，则类似增添新的key-value；若key重复，则key对应的value会被覆盖

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

Info_new = {'stu4':'Jack','stu5':'Tony','stu6':'Tom'}

Info.update(Info_new)

print(Info)# =>{'stu1': 'LiLei', 'stu2': 'HanMeiMei', 'stu3': 'XiaoMing', 'stu4': 'Jack', 'stu5': 'Tony', 'stu6': 'Tom'}

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

Info_new = {'stu1':'Jack','stu5':'Tony','stu6':'Tom'}

Info.update(Info_new)

print(Info)# =>{'stu1': 'Jack', 'stu2': 'HanMeiMei', 'stu3': 'XiaoMing', 'stu5': 'Tony', 'stu6': 'Tom'}

其他语法

循环输出所有的key

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

for key in Info:

    print(key)

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

for key in Info.keys():

    print(key)

循环输出所有的value

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

for value in Info.values():

    print(value)

循环输出所有的key-value

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

for key in Info:

    print(key,Info[key])

del：删除指定的key，若key不存在，则报错

Info = {'stu1':'LiLei','stu2':'HanMeiMei','stu3':'XiaoMing'}

del Info['stu1']

print(Info)# =>{'stu2': 'HanMeiMei', 'stu3': 'XiaoMing'}

del Info['stu4']# =>报错

巴特西

dict的特性和基本语法——python3.6

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