字典：

字典取值快，通过key去找

字典是无序的，因为其不是按照顺序进行取值的，是按照key和value进行取值的

1、定义

info={}   #定义空字典

info={"name":"zhaozhao","age":23,"sex":"男"}  #定义字典

2、增加KEY

增加KEY两种方式：

info["key"]=value   # 字典该KEY存在改变其值，不存该KEY则增加该KEY

info.setdefault(key,value) #字典该KEY存在不改变其值，不存该KEY则增加该KEY

info={"name":"zhaozhao"}

info["sex"]=23info["name"]="zhaozhao1"

print(info)

D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py

{'name': 'zhaozhao1', 'sex': 23}

info={"name":"zhaozhao"}

info.setdefault("sex","男")

info.setdefault("name","zhaozhao2")print(info)

D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py

{'name': 'zhaozhao', 'sex': '男'}

3、删除

pop：指定key删除，key不存在会报错

del：指定key删除，key不存在会报错

popitem：随机返回并删除字典中的一对键和值。 如果字典已经为空，却调用了此方法，就报出KeyError异常

info={"name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}

info.pop("name")print("pop:",info)del info["sex"]print("del:",info)

info.popitem()print("popitem:",info)

pop: {'sex': '男', 'age': '10', '班级': '1班', '成绩': '90'}del: {'age': '10', '班级': '1班', '成绩': '90'}

popitem: {'age': '10', '班级': '1班'}

4、字典取值

如果key存在，2者没有什么区别，如果key不存在，info["key"]这种方式程序报错，info.get("phone")这种方式返回none

info={"name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}print(info["name"])print(info.get('name'))print("=========================")print(info.get('ab'))print(info["ab"])

5、获取key集合，获取value集合

print(info.keys()) #获取字典所有的key

print(info.values()) #获取字典所有的value

info={"name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}print(info.keys())print(info.values())

D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py

dict_keys(['name', 'sex', 'age', '班级', '成绩'])

dict_values(['zhaozhao', '男', '10', '1班', '90'])

6、判断key是否存在于字典

info.haskey("key") #python2

key in info #python3用于这种方式判断key是否存在于字典

info={"name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}

cname='name'dname='zhaozhao'

#key是否在key集合中

if cname ininfo.keys():print("sucess")#value是否在values集合中

if dname ininfo.values():print("sucess2")#key是否在字典中

if cname ininfo:print("sucess3")

7、一个字典追加另一个字典

info={"name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}

info2={"score":"89"}

info.update(info2)print(info)

D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py

{'name': 'zhaozhao', 'sex': '男', 'age': '10', '班级': '1班', '成绩': '90', 'score': '89'}

8、循环字典值

info={"name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}for k ininfo:print("%s => %s"%(k,info[k]))for k,v ininfo.items():print("%s => %s"%(k,v))

这两种第一种性能上说快一些，第二种性能弱一些