class Demo:
    alive =True
    _username = "protected"
    __password = "private"
    def __init__(self,name):
        self.name = name

    @property
    def password(self):
        return self.__password

    @password.setter
    def password(self , new_password):
        if len(new_password) >= 8:
            self.__password = new_password
        else:
            print("密码长度不符合要求")

if __name__ =="__main__":
    print(Demo.alive)
    print(Demo._username)
    print(Demo.__dict__)

    obj = Demo(name= "zhaoxiaobo")
    print(obj.alive)
    print(obj._username)
    #print(obj.__password)

obj.password="123345666"
print(obj.password)