《Effective Python》笔记——第4章 元类及属性

一、用属性取代get和set方法

常规的get和set方法如下：

class OldResistor():
    def __init__(self, ohms):
        self.__ohms = ohms

    def get_ohms(self):
        return self.__ohms

    def set_ohms(self, ohms):
        self.__ohms = ohms


if __name__ == '__main__':
    r0 = OldResistor(50e3)
    print(r0.get_ohms())
    r0.set_ohms(10e3)
    print(r0.get_ohms())

@property装饰器getter，和setter方法协同工作

class Resistor():
    def __init__(self, ohms):
        self.ohms = ohms
        self.voltage = 0
        self.current = 0


class VolResistor(Resistor):
    def __init__(self, ohms):
        super().__init__(ohms)  # 继承父类的变量
        self.__vol = 100  # __开头的变量为内部变量，无法在外部引用

    @property   # getter设置voltage属性
    def voltage(self):
        return self.__vol

    @voltage.setter
    def voltage(self, voltage):
        self.__vol = voltage
        self.current = self.__vol / self.ohms


if __name__ == '__main__':
    r1 = Resistor(50e3)
    r1.ohms = 10e3  # public属性
    r1.ohms += 5e3
    print(r1.ohms)

    r2 = VolResistor(10)
    print(r2.voltage)   # getter属性，不会执行voltage的setter方法，不会更新current属性
    print(r2.current)
    r2.voltage = 100    # voltage属性赋值时，将会执行voltage的setter方法，更新current属性
    print(r2.current)

二、考虑用@property来代替属性重构

pass

三、用描述符来改写需要服用的@property方法

__get__
__set__

四、__getattr__、__getattribute__、__setattr__实现按需生成的属性

pass

五、元类

__new__

pass