code: def requires(self):
          
          if self.use_spark:
              return AggregateArtistsSpark(self.date_interval)
          else:
              return AggregateArtists(self.date_interval)
docs: This task's dependencies:
  
          * :py:class:`~.AggregateArtists` or
          * :py:class:`~.AggregateArtistsSpark` if :py:attr:`~/.Top10Artists.use_spark` is set.
  
          :return: object (:py:class:`luigi.task.Task`)