code: def _normalised_python(self):
          
          dx = (self.screen.width / float(len(self.points)))
          oy = (self.screen.height)
          for x, point in enumerate(self.points):
              y = (point - self.minimum) * 4.0 / self.extents * self.size.y
              yield Point((
                  dx * x,
                  min(oy, oy - y),
              ))
docs: Normalised data points using pure Python.