docs: def pointlist(points, sr):
      """Convert a list of the form [[x, y] ...] to a list of Point instances
         with the given x, y coordinates."""
      assert all(isinstance(pt, Point) or len(pt) == 2 
                 for pt in points), "Point(s) not in [x, y] form"
      return [coord if isinstance(coord, Point) 
                    else Point(coord[0], coord[1], sr)
              for coord in points]