Python之元类

class ItemMetaClass(type):
    # cls 代表被动态修改的类
    # name 代表被动态修改的类名
    # bases 代表被动态修改的类的所有父类
    # attr 代表被动态修改的类的所有属性、方法组成的字典
    def __new__(cls, name, bases, attrs):
        attrs[‘cal_price‘] = lambda self: self.price * self.discount
        return type.__new__(cls, name, bases, attrs)


class Book(metaclass=ItemMetaClass):
    __slots__ = [‘name‘, ‘price‘, ‘_discount‘]
    def __init__(self, name, price):
        self.name = name 
        self.price = price
    @property
    def discount(self):
        return self._discount
    @discount.setter
    def discount(self, discount):
        self._discount = discount

class CellPhone(metaclass=ItemMetaClass):
    __slots__ = [‘price‘, ‘_discount‘]
    def __init__(self, price):
        self.price = price
    @property
    def discount(self):
        return self._discount
    @discount.setter
    def discount(self, discount):
        self._discount = discount

b = Book(‘九年级数学上‘, 89)
b.discount = 0.76
print(b.cal_price())
cp = CellPhone(2399)
cp.discount = 0.85
print(cp.cal_price())