python dict 字典
CRUD(创建，读取，更新，删除)
键值对，无序，键唯一，且是字符串，不可变，因此是可hash对象
1，创建
2，读取 （按键、值，键值进行查询）
3，更新 用的比较少
4，删除

1，创建

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(type(userinfo1))
print(userinfo1)

<class ‘dict’>
{‘id’: 1, ‘name’: ‘zhangsan’, ‘ages’: 18, ‘work’: ‘sales’}
2，读取 （按键、值，键值进行查询）
#按键读取 get

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(userinfo1["name"]) #直接获取

zhangsan

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(userinfo1.get("name"))  #通过键取到对应的值

zhangsan

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(userinfo1.keys())

dict_keys([‘id’, ‘name’, ‘ages’, ‘work’])
#按值取

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(userinfo1.values())

dict_values([1, ‘zhangsan’, 18, ‘sales’])
#按键值读取

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(userinfo1.items())

dict_items([(‘id’, 1), (‘name’, ‘zhangsan’), (‘ages’, 18), (‘work’, ‘sales’)])
#用循环获取所有key,value

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
for key,value in userinfo1.items():
    print(key,value)
print(userinfo1)

id 1
name zhangsan
ages 18
work sales
{‘id’: 1, ‘name’: ‘zhangsan’, ‘ages’: 18, ‘work’: ‘sales’}
3，更新

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
userinfo1["mail"]="zhangsan@qq.com"  #在最后增加一个邮箱的键值对
print(userinfo1)

{‘id’: 1, ‘name’: ‘zhangsan’, ‘ages’: 18, ‘work’: ‘sales’, ‘mail’: ‘zhangsan@qq.com’}
4，删除 pop，（pop,popitem?）

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(userinfo1.pop("ages")) #删除key=ages的键值对
print(userinfo1)

18
{‘id’: 1, ‘name’: ‘zhangsan’, ‘work’: ‘sales’}

#清空字典

userinfo1={"id":1,"name":"zhangsan","ages":18,"work":"sales"}
print(userinfo1.clear())  #清空字典
print(userinfo1)

None
{}