python-字典
字典dict
http://www.runoob.com/python3/python3-dictionary.html
字典是另一种可变容器模型，且可存储任意类型对象。
字典的每个键值对用冒号(:)分割，每个对之间用逗号(,)分割，整个字典包括在花括号({})中 ,格式如下所示：
d = {key1 : value1, key2 : value2 } dict = {'Alice': '2341', 'Beth': '9102', 'Cecil': '3258'}
键必须是唯一的，但值则不必。值可以取任何数据类型，但键必须是不可变的，只能是字符串，数字或元组。
创建
dict01={"name":"毛奇","age":42,"sex":"男"}
dict02={"name":"李佩琪","age":41,"sex":"女"}
dict03={"name":"马翔宇","age":32,"sex":"男"}
添加或修改
dict01={"name":"毛奇","age":42,"sex":"男"}
dict01["money"]=100 #添加--尾部添加
#money是键 100是值
dict01["age"]=43 #修改值
#注意：键已经存在，就修改值；如果不存在就添加
print(dict01)
dict01={"name":"毛奇","age":42,"sex":"男"}
dict02={"id":"1001","身高":171}
dict01.update(dict02) #在尾部添加另一个字典的内容
print(dict01)
读取值
dict01={"name":"毛奇","age":42,"sex":"男"}
if "age" in dict01:
i=dict01["age"] #如果键不存在会报错
print(i)
dict01={"name":"毛奇","age":42,"sex":"男"}
i=dict01.get('name', "键不存在")
i1=dict01.get('Name', "键不存在")
""""
参数1 键名
字典中要是存在键 就返回键对应的值；要是不存在，就返回参数2
参数2 默认是None
"""
print(i)
print(i1)
dict01={"name":"毛奇","age":42,"sex":"男"}
i=aa= dict01.setdefault('name', "祝欢")
i1=dict01.setdefault('Name', "键不存在")
""""
参数1 键名
字典中要是存在键 就返回键对应的值；
要是不存在，就返回参数2,并且在字典的尾部添加这个键值对
参数2 默认是None
"""
print(i)
print(i1)
print(dict01)
删除
dict01={"name":"毛奇","age":42,"sex":"男"}
del dict01["age"] #删除键值对
print(dict01)
dict01={"name":"毛奇","age":42,"sex":"男"}
pop=dict01.pop('name') #删除键值对,返回被删除的值，键要是不存在就抛出错误
print(dict01,pop)
dict01={"name":"毛奇","age":42,"sex":"男"}
pop=dict01.pop('Name',"不存在") #删除键值对,返回被删除的值，键要是不存在就返回参数2
print(dict01,pop)
dict01={"name":"毛奇","age":42,"sex":"男"}
pop=dict01.popitem() #删除最后的键值对
#返回被删除键值对的元组
print(dict01,pop)
dict01={"name":"毛奇","age":42,"sex":"男"}
del dict01 #删除字典
清空字典
dict.clear()
返回字典的长度
x=len(dict)
返回键值对的总数
返回所有键和值
dict01={"name":"毛奇","age":42,"sex":"男"}
a=dict01.keys() #返回所有键
#返回值：列表
b=dict01.values() #返回所有值
#返回值：列表
print(a)
print(b)
遍历字典
dict01={"name":"毛奇","age":42,"sex":"男"}
for item in dict01: #item是键
print(item)
dict01={"name":"毛奇","age":42,"sex":"男"}
for item in dict01.keys(): #item键
print(item)
dict01={"name":"毛奇","age":42,"sex":"男"}
for item in dict01.values(): #item值
print(item)
dict01={"name":"毛奇","age":42,"sex":"男"}
for item in dict01.items(): #item时键值对元组
print(item)
dict01={"name":"毛奇","age":42,"sex":"男"}
for key,value in dict01.items(): #key是键，value是值
print(key,value)
字典转换成列表
dict01={"name":"毛奇","age":42,"sex":"男"}
lb=list(dict01) #返回键名列表
print(lb)
dict01={"name":"毛奇","age":42,"sex":"男"}
lb=list(dict01.values()) #返回值列表
print(lb)
dict01={"name":"毛奇","age":42,"sex":"男"}
lb=list(dict01.items()) #返回键值对的元组列表
print(lb)
列表转换成字典
lb=[('name', '毛奇'), ('age', 42), ('sex', '男')] dict01=dict(lb) #列表转换成字典 print(dict01)
练习
1.把两个列表组合成字典
#把两个列表组合成字典 list01=["毛奇","李佩霞","马翔宇"] list02=[42,43,31] dict01={} for i in range(len(list01)): key=list01[i] value=list02[i] dict01[key]=value print(dict01)
2.多层字典
dict_info={"北京":{"景区":["长城","故宫"],"美食":["烤鸭","豆汁焦圈","炸酱面"]},"四川":{"景区":["九寨沟","峨眉山"],"美食":["火锅","兔头"]}}
#练习1：打印北京的第一个景区
print(dict_info["北京"]["景区"][0])
#练习2：打印所有城市
print(dict_info.keys())
#练习3：打印所有城市的所有美食(一行一个)
for item in dict_info.keys():
print(dict_info[item]["美食"])
字典推导式
list01=["毛奇","李佩霞","马翔宇"] list02=[42,41,31] dict01={list01[i]:list02[i] for i in range(len(list01))} print(dict01)
其它格式：看推导式
练习：颠倒字典的键和值
dict01={'毛奇': 42, '李佩霞': 41, '马翔宇': 31}
dict02={ value:key for key,value in dict01.items() }
print(dict02)
