code: def add_angles(self, indexes, deg=False, cossin=False, periodic=True):
          
          from .angles import AngleFeature
          indexes = self._check_indices(indexes, pair_n=3)
          f = AngleFeature(self.topology, indexes, deg=deg, cossin=cossin,
                           periodic=periodic)
          self.__add_feature(f)
docs: Adds the list of angles to the feature list
  
          Parameters
          ----------
          indexes : np.ndarray, shape=(num_pairs, 3), dtype=int
              an array with triplets of atom indices
          deg : bool, optional, default = False
              If False (default), angles will be computed in radians.
              If True, angles will be computed in degrees.
          cossin : bool, optional, default = False
              If True, each angle will be returned as a pair of (sin(x), cos(x)).
              This is useful, if you calculate the mean (e.g TICA/PCA, clustering)
              in that space.
          periodic : bool, optional, default = True
              If `periodic` is True and the trajectory contains unitcell
              information, we will treat dihedrals that cross periodic images
              using the minimum image convention.