Python之元类

Posted 2020-11-22 zhzhang

 

如果希望创建某一批类全部具有某种特征，则可通过metaclass来实现。使用metaclass可以在创建类时动态修改类定义。

为了使用metaclass动态修改类定义，程序需要先定义metaclass，metaclass应该继承type类，并重写new方法。

 

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())

 

谢谢！