code: def DeregisterHelper(cls, helper_class):
      
      helper_name = helper_class.NAME.lower()
      if helper_name not in cls._helper_classes:
        raise KeyError('Helper class not set for name: {0:s}.'.format(
            helper_class.NAME))
  
      del cls._helper_classes[helper_name]
docs: Deregisters a helper class.
  
      The helper classes are identified based on their lower case name.
  
      Args:
        helper_class (type): class object of the argument helper.
  
      Raises:
        KeyError: if helper class is not set for the corresponding name.