code: def segment(self):
          
          if len(self.segment_list) == 1:
              return self.segment_list[0]
          else:
              err = "self.segment_list must only contain one segment to access"
              err += " the segment property. %s." %(str(self.segment_list),)
              raise TypeError(err)
docs: If only one segment in the segmentlist this will be that segment.
          Otherwise an error is raised.