old_contents: ##  Abstract base class for all input devices
  class InputDevice(object):
      def __init__(self):
          super(InputDevice, self).__init__()
      
      
  
new_contents: from Cura.Signal import Signal
  
  ##  Abstract base class for all input devices
  class InputDevice(object):
      def __init__(self):
          super(InputDevice, self).__init__()
          self.event = Signal()
  
      ## Signal. Emitted whenever the device produces an event.
      #  \param event The event that is emitted.
      event = None
  
subject: Add an event signal to InputDevice