code: def get_angle(self, i: int, j: int, k: int) -> float:
          
          v1 = self[i].coords - self[j].coords
          v2 = self[k].coords - self[j].coords
          return get_angle(v1, v2, units="degrees")
docs: Returns angle specified by three sites.
  
          Args:
              i: Index of first site.
              j: Index of second site.
              k: Index of third site.
  
          Returns:
              Angle in degrees.