docs: def rise_per_residue(self):
          """The rise per residue at each point on the Primitive.
  
          Notes
          -----
          Each element of the returned list is the rise per residue,
          at a point on the Primitive. Element i is the distance
          between primitive[i] and primitive[i + 1]. The final value
          is None.
          """
          rprs = [distance(self[i]['CA'], self[i + 1]['CA'])
                  for i in range(len(self) - 1)]
          rprs.append(None)
          return rprs