code: def _check_rot_sym(self, axis):
          
          min_set = self._get_smallest_set_not_on_axis(axis)
          max_sym = len(min_set)
          for i in range(max_sym, 0, -1):
              if max_sym % i != 0:
                  continue
              op = SymmOp.from_axis_angle_and_translation(axis, 360 / i)
              rotvalid = self.is_valid_op(op)
              if rotvalid:
                  self.symmops.append(op)
                  self.rot_sym.append((axis, i))
                  return i
          return 1
docs: Determines the rotational symmetry about supplied axis.  Used only for
          symmetric top molecules which has possible rotational symmetry
          operations > 2.