code: def radii_of_curvature(self):
          
          rocs = []
          for i, _ in enumerate(self):
              if 0 < i < len(self) - 1:
                  rocs.append(radius_of_circumcircle(
                      self[i - 1]['CA'], self[i]['CA'], self[i + 1]['CA']))
              else:
                  rocs.append(None)
          return rocs
docs: The radius of curvature at each point on the Polymer primitive.
  
          Notes
          -----
          Each element of the returned list is the radius of curvature,
          at a point on the Polymer primitive. Element i is the radius
          of the circumcircle formed from indices [i-1, i, i+1] of the
          primitve. The first and final values are None.