code: def DeregisterSourceType(cls, source_type_class):
      
      if source_type_class.TYPE_INDICATOR not in cls._source_type_classes:
        raise KeyError(
            'Source type not set for type: {0:s}.'.format(
                source_type_class.TYPE_INDICATOR))
  
      del cls._source_type_classes[source_type_class.TYPE_INDICATOR]
docs: Deregisters a source type.
  
      Source types are identified based on their type indicator.
  
      Args:
        source_type_class (type): source type.
  
      Raises:
        KeyError: if a source type is not set for the corresponding type
            indicator.