python字典的操作讲解

字典的出现：介于列表存储信息少，增删查改速度慢，出现了字典，用来存储更多种类信息，字典是一种key-value存储，key值不可变，可以是整数，字符串，不能是list，通过key值找value，每个key值只对应一个value.

字典定义：

(1)basketballplayer={'01':"Sun Dali",

'02':"Sun Xiaowei",

'03':"Da Ming",

'04':"Kobe",

"05":"ZhenMusi",

"06":"Blackmen",

"07":"Wang Dalu"}

(2)soccerplayer={"01":"David",

"08":"Li Yi",

"03":"Li Jinyu",

"09":"Wang Dalei"}

字典输出：print(basketballplayer) 结果为乱序

字典用法：(1)通过key找value print(basketballplayer['05'])

(2)通过key修改value basketballplayer['01']='Xiaowei'

print(basketballplayer['01'])

(3)通过不存在的key添加新的key value 用法同(2)

(4)删除某个key-value del basketballplayer['01']

basketballplayer.pop('02')

basketballplayer.popitem() #随便删一个

(5)查找某个value print('04' in basketballplayer) #首先通过key值判断是否在字典里

print(basketballplayer.get('04')) #上句返回真，则取出value

(6)打印所有value值 print(basketballplayer.values())

(7)打印所有key值 print(basketballplayer.keys())

(8)soccerplayer字典与basketballplayer字典合并，且有交叉用 soccerplayer字典更新basketballplayer字典 basketballplayer.update(soccerplayer)

print(basketballplayer)

(9)初始化一个value值相同的字典 newdict=dict.fromkeys([1,2,3],"cups")

print(newdict)

(10)修改(9)方式字典中的值 newdict=dict.fromkeys([1,2,3],[520,{"flower":"rose"},1314])

newdict[2][1]["flower"]="lily"

newdict[3][2]=666

print(newdict)

(11)字典变列表 print(basketballplayer.items())

(12)字典循环 for i in basketballplayer: #直接循环，i为key

print(i,basketballplayer[i])

for k,v in basketballplayer.items(): #将字典转为列表在循环，比直接循环费时

print(k,v)

(13)setdefault()用法 basketballplayer.setdefault("04","Xiaohua") #找到04号则不变否则创建新的key value

print(basketballplayer)