text: from duck import Duck
  
  
  class MallardDuck(Duck):
      """Concrete implementation of a MallardDuck."""
  
      def __init__(self, fly_behavior, quack_behavior):
          super().__init__(fly_behavior, quack_behavior)
  
      def display(self):
          print('I am a mallard duck!')
  
      __slots__ = (
          '_fly_behavior',
          '_quack_behavior',
      )
  