text: # useful exception for going into sleep
  class GoodNite(Exception):
      """ exception for when the lights should be off """
      pass
  
  class EndSession(Exception):
      """ exception for when a session should terminate """
      pass
  
  class EndBlock(Exception):
      """ exception for when a block should terminate """
      pass
  
  ## defining Error classes for operant HW control
  class Error(Exception):
      '''base class for exceptions in this module'''
      pass
  
  class InterfaceError(Exception):
      '''raised for errors with an interface.
  
      this should indicate a software error, like difficulty 
      connecting to an interface
      '''
      pass
  
  class ComponentError(Exception):
      '''raised for errors with a component.
  
      this should indicate a hardware error in the physical world, 
      like a problem with a feeder.
  
      this should be raised by components when doing any internal 
      validation that they are working properly
  
      '''
      pass
  