如果我们想要限制实例的属性，Python允许在定义class的时候，定义一个特殊的slots变量，来限制该class实例能添加的属性。
使用slots要注意，slots定义的属性仅对当前类实例起作用，对继承的子类是不起作用的
除非在子类中也定义slots，这样，子类实例允许定义的属性就是自身的slots加上父类的slots。

# coding:utf-8
class Player(object):
    def __init__(self, uid, name, stat=0, level=1):
        self.uid = uid
        self.name = name
        self.stat = stat
        self.level = level


class Player2(object):
    __slots__ = ['uid', 'name', 'stat', 'level', 'sex']

    def __init__(self, uid, name, stat=0, level=1):
        self.uid = uid
        self.name = name
        self.stat = stat
        self.level = level


class Player3(Player2):
    def __init__(self, uid, name):
        super(Player3, self).__init__(uid, name)


class Player4(Player2):
    __slots__ = ['age']

    def __init__(self, uid, name):
        super(Player4, self).__init__(uid, name)

# 创建实例
p1 = Player('001', 'Jim')
p2 = Player2('002', 'Jim2')
p3 = Player3('003', 'Jim3')
p4 = Player4('004', 'Jim4')

# p1实例
print(p1.name)  # jim
p1.age = 16
print(p1.age)  # 16

# p2实例
print(p2.name)  # Jim2
p2.sex = 'boy'
print(p2.sex)  # boy
# p2.age = 16
# print(p2.age)  # 错误异常 AttributeError

# p3实例 __slots__定义的属性仅对当前类实例起作用，对继承的子类是不起作用的
print(p3.name)  # Jim3
p3.age = 16
print(p3.age)  # 16

# p4实例 
# 子类中也定义__slots__，这样，子类实例允许定义的属性就是自身的__slots__加上父类的__slots__
print(p4.name)  # Jim4
p4.age = 16
print(p4.age)  # 16
p4.sex = 'girl'
print(p4.sex)  # girl
# p4.date = '2019'
# print(p4.date)  # 错误异常 AttributeError