code: def get_singleton(self):
          
          only_value = None
          for value in six.itervalues(self.ordered_dict):
              # This loop will raise if it runs more than once.
              if only_value is not None:
                  raise ValueError("%r is not a singleton." % self)
  
              only_value = value
  
          if only_value is self.__UnsetSentinel or only_value is None:
              raise ValueError("%r is empty." % self)
  
          return only_value
docs: If the row only has one column, return that value; otherwise raise.
  
          Raises:
              ValueError, if count of columns is not 1.