code: def add_track(self, track):
          
          if not hasattr(track, 'bars'):
              raise UnexpectedObjectError("Unexpected object '%s', "
                      "expecting a mingus.containers.Track object" % track)
          self.tracks.append(track)
          self.selected_tracks = [len(self.tracks) - 1]
docs: Add a track to the composition.
  
          Raise an UnexpectedObjectError if the argument is not a
          mingus.containers.Track object.