python 设计模式（十三） 外观模式（facade pattern）

外观模式又称包装外观模式，从字面意思很好理解，即对某一类复杂操作的封装。封装出更直观通用的接口类，然后给客户端调用。比如，你离开家，要关上灯，关上空调，关上电源等，这是一系列很麻烦的操作，因此，你可以把这一系列的操作封装到一个类中，然后让客户端调用。

举例如下：

class Equipment(object):

    def __init__(self):
        self.name = ''
        self.state = 'open'

    def turn_off(self):
        if self.state == 'closed':
            print('%s has been shut down')
        else:
            self.state = 'closed'
            print('%s is closed' % self.name)


class Lamp(Equipment):

    def __init__(self):
        super().__init__()
        self.name = 'lamp'


class AirConditioner(Equipment):

    def __init__(self):
        super().__init__()
        self.name = 'air_conditioner'


class OldClient(object):

    def __init__(self, lamp, air_conditioner):
        self.lamp = lamp
        self.air_conditioner = air_conditioner

    def leave_home(self):
        self.lamp.turn_off()
        self.air_conditioner.turn_off()


class FacadeEquipment(object):
    def __init__(self, lamp, air_conditioner):
        self.lamp = lamp
        self.air_conditioner = air_conditioner

    def close(self):
        self.lamp.turn_off()
        self.air_conditioner.turn_off()


class FacadeClient(object):
    def __init__(self, equipments):
        self.equipments = equipments

    def leave_home(self):
        self.equipments.close()


if __name__ == '__main__':
    print('old pattern')
    lamp = Lamp()
    air_conditioner = AirConditioner()
    old_client = OldClient(lamp, air_conditioner)
    old_client.leave_home()
    print('facade pattern')
    facade_equipment = FacadeEquipment(lamp, air_conditioner)
    facade_client = FacadeClient(facade_equipment)
    facade_client.leave_home()

结果如下

old pattern
lamp is closed
air_conditioner is closed
facade pattern
%s has been shut down
%s has been shut down

上述代码实现了lamp,airconditioner类，这两个类继承自equipment,oldclient直接调用了这两个类的实例，耦合性比较强。采用外观模式后，FacadeEquipment对lamp和airconditioner进行了封装，实现了客户端与lamp和airconditioner解耦，同时，FacadeEquipment封装出了close方法，已供新的外观模式客户端调用