docs: def create_ranking(ranking_tuples):
          """
          Create and return a string suitable for the rankings
          field when given tuples of choices and rankings.
          Parameters:     ranking_tuples should be an iterable
                              of tuples of form (choice, ranking)
          """
          return ",".join([str(r) for c, r in sorted(
                  ranking_tuples,
                  key=lambda x: x[0].pk
                  )])