code: def read_units(self, fid):
          
          lin = self.read_line(fid)                   
          while lin[0] != ':':
              parts = lin.split()
              if parts[0]=='mass':
                  self.mass = float(parts[1])
              elif parts[0]=='length':
                  self.length = float(parts[1])
              elif parts[0]=='angle':
                  self.angle = parts[1]
              lin = self.read_line(fid)
          return lin
docs: Read units from an acclaim skeleton file stream.