text: import Command
  
  class LightCommand(Command.Command) :    
      def __init__(self, light) :
          self.light = light
          self.prev_level = None
          
      def undo(self) :
          self.light.dim(self.prev_level)
  
  class DimmerLightOffCommand(LightCommand) :
      def __init__(self, light) :
          self.light = light
      
      def execute(self) :
          self.prev_level = self.light.level
          self.level.off()
  
  class DimmerLightOnCommand(LightCommand) :
      def __init__(self, light) :
          self.light = light
      
      def execute(self) :
          self.prev_level = self.light.level
          self.level.dim(75)
  
  class LightOffCommand(LightCommand) :
      def __init__(self, light) :
          self.light = light
      
      def execute(self) :
          self.prev_level = self.light.level
          self.light.off()
  
  class LightOnCommand(LightCommand) :
      def __init__(self, light) :
          self.light = light
      
      def execute(self) :
          self.prev_level = self.light.level
          self.light.on()
  