Python 外观模式

外观模式模式为子系统中的一组接口提供了统一的接口。它定义了任何子系统都可以使用的高级接口。

Facade类知道哪个子系统负责请求。

1. 如何设计外观模式？

现在让我们看看如何设计外观模式。

# Filename : example.py
# Date : 2020-08-22
class _IgnitionSystem(object):
    @staticmethod
    def produce_spark():
        return True
class _Engine(object):
    def __init__(self):
        self.revs_per_minute = 0
    def turnon(self):
        self.revs_per_minute = 2000
    def turnoff(self):
        self.revs_per_minute = 0
class _FuelTank(object):
    def __init__(self, level=30):
        self._level = level
    @property
    def level(self):
        return self._level
    @level.setter
    def level(self, level):
        self._level = level
class _DashBoardLight(object):
    def __init__(self, is_on=False):
        self._is_on = is_on
    def __str__(self):
        return self.__class__.__name__
    @property
    def is_on(self):
        return self._is_on
    @is_on.setter
    def is_on(self, status):
        self._is_on = status
    def status_check(self):
        if self._is_on:
            print("{}: ON".format(str(self)))
        else:
            print("{}: OFF".format(str(self)))
class _HandBrakeLight(_DashBoardLight):
    pass
class _FogLampLight(_DashBoardLight):
    pass
class _Dashboard(object):
    def __init__(self):
        self.lights = {"handbreak": _HandBrakeLight(), "fog": _FogLampLight()}
    def show(self):
        for light in self.lights.values():
            light.status_check()
# Facade
class Car(object):
    def __init__(self):
        self.ignition_system = _IgnitionSystem()
        self.engine = _Engine()
        self.fuel_tank = _FuelTank()
        self.dashboard = _Dashboard()
    @property
    def km_per_litre(self):
        return 17.0
    def consume_fuel(self, km):
        litres = min(self.fuel_tank.level, km / self.km_per_litre)
        self.fuel_tank.level -= litres
    def start(self):
        print("\nStarting...")
        self.dashboard.show()
        if self.ignition_system.produce_spark():
            self.engine.turnon()
        else:
            print("Can't start. Faulty ignition system")
    def has_enough_fuel(self, km, km_per_litre):
        litres_needed = km / km_per_litre
        if self.fuel_tank.level > litres_needed:
            return True
        else:
            return False
    def drive(self, km = 100):
        print("\n")
        if self.engine.revs_per_minute > 0:
            while self.has_enough_fuel(km, self.km_per_litre):
                self.consume_fuel(km)
                print("Drove {}km".format(km))
                print("{:.2f}l of fuel still left".format(self.fuel_tank.level))
        else:
            print("Can't drive. The Engine is turned off!")
    def park(self):
        print("\nParking...")
        self.dashboard.lights["handbreak"].is_on = True
        self.dashboard.show()
        self.engine.turnoff()
    def switch_fog_lights(self, status):
        print("\nSwitching {} fog lights...".format(status))
        boolean = True if status == "ON" else False
        self.dashboard.lights["fog"].is_on = boolean
        self.dashboard.show()
    def fill_up_tank(self):
        print("\nFuel tank filled up!")
        self.fuel_tank.level = 100
# the main function is the Client
def main():
    car = Car()
    car.start()
    car.drive()
    car.switch_fog_lights("ON")
    car.switch_fog_lights("OFF")
    car.park()
    car.fill_up_tank()
    car.drive()
    car.start()
    car.drive()
if __name__ == "__main__":
    main()

输出

上面的程序生成以下输出：

Starting...
_HandBrakeLight: OFF
_FogLampLight: OFF
Drove 100km
24.12l of fuel still left
Drove 100km
18.24l of fuel still left
Drove 100km
12.35l of fuel still left
Drove 100km
6.47l of fuel still left
Drove 100km
0.59l of fuel still left
Switching ON fog lights...
_HandBrakeLight: OFF
_FogLampLight: ON
Switching OFF fog lights...
_HandBrakeLight: OFF
_FogLampLight: OFF
Parking...
_HandBrakeLight: ON
_FogLampLight: OFF
Fuel tank filled up!
Can't drive. The Engine is turned off!
Starting...
_HandBrakeLight: ON
_FogLampLight: OFF
Drove 100km
94.12l of fuel still left
Drove 100km
88.24l of fuel still left
Drove 100km
82.35l of fuel still left
Drove 100km
76.47l of fuel still left
Drove 100km
70.59l of fuel still left
Drove 100km
64.71l of fuel still left
Drove 100km
58.82l of fuel still left
Drove 100km
52.94l of fuel still left
Drove 100km
47.06l of fuel still left
Drove 100km
41.18l of fuel still left
Drove 100km
35.29l of fuel still left
Drove 100km
29.41l of fuel still left
Drove 100km
23.53l of fuel still left
Drove 100km
17.65l of fuel still left
Drove 100km
11.76l of fuel still left
Drove 100km
5.88l of fuel still left
Drove 100km
0.00l of fuel still left

说明

该程序是根据场景设计的。它是启动汽车或任何行驶中的车辆的引擎的过程。如果您遵守该代码，则它包含相关的驱动，停车和消耗燃料的功能。