Python Design Patterns 简明教程
Python Design Patterns - Facade
外观设计模式为子系统中的一组接口提供了一个统一接口。它定义了一个任何子系统都可以使用的更高级别接口。
门面类知道哪个子系统对请求负责。
How to design a facade pattern?
让我们现在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()