code: def _key(cls, obs):
          '''Provides sorting index for Observation objects'''
          if not isinstance(obs, Observation):
              raise JamsError('{} must be of type jams.Observation'.format(obs))
  
          return obs.timf _key(cls, obs):
          '''Provides sorting index for Observation objects'''
          if not isinstance(obs, Observation):
              raise JamsError('{} must be of type jams.Observation'.format(obs))
  
          return obs.time
docs: Provides sorting index for Observation objects