code: def as_xyz_string(self):
          
          xyz = ['x', 'y', 'z']
          strings = []
  
          # test for invalid rotation matrix
          if not np.all(np.isclose(self.rotation_matrix,
                                   np.round(self.rotation_matrix))):
              warnings.warn('Rotation matrix should be integer')
  
          return transformation_to_string(self.rotation_matrix, translation_vec=self.translation_vector, delim=", ")
docs: Returns a string of the form 'x, y, z', '-x, -y, z',
          '-y+1/2, x+1/2, z+1/2', etc. Only works for integer rotation matrices