code: def get_ranking(self, alt):
          
          if self.alts_to_ranks is None:
              raise ValueError("Aggregate ranking must be created first")
          try:
              rank = self.alts_to_ranks[alt]
              return rank
          except KeyError:
              raise KeyError("No alternative \"{}\" found in ".format(str(alt)) +
                             "the aggregate ranking")
docs: Description:
              Returns the ranking of a given alternative in the
              computed aggregate ranking.  An error is thrown if
              the alternative does not exist.  The ranking is the
              index in the aggregate ranking, which is 0-indexed.
          Parameters:
              alt: the key that represents an alternative