Python 设计模式 - 门面模式

• 

  简述

  门面设计模式为子系统中的一组接口提供统一的接口。它定义了任何子系统都可以使用的更高级别的接口。

  门面类知道哪个子系统负责请求。
• 

  如何设计门面模式？

  现在让我们看看如何设计门面模式。

  
  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

  上述程序生成以下输出 -

  

  解释

  该程序是根据场景设计的。这是启动汽车或任何驾驶车辆的发动机。如果您观察代码，它还包括与驾驶、停车和消耗燃料相关的功能。