code: def _max_min(self):
          
          dtbl = self.datatable
  
          objs = object_session(self)
          if isinstance(dtbl, Table):
              return objs.query(func.max(dtbl.c.indx).label("max_indx"),
                                func.min(dtbl.c.indx).label("min_indx")).one()
          else:
              raise Exception("Symbol has no datatable")
docs: Returns
          -------
          A tuple consisting of (max, min) of the index.