Python设计模式外观模式

Facade设计模式为子系统中的一组接口提供了一个统一的接口。它定义了一个更高层次的接口，任何子系统都可以使用。

一个外观类知道哪个子系统负责一个请求。

如何设计一个外观模式

现在让我们来看看如何设计一个外观模式。

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()