code: def sequence(self, per_exon=False):
          
          db = self.db
          if not per_exon:
              start = self.txStart + 1
              return _sequence(db, self.chrom, start, self.txEnd)
          else:
              # TODO: use same strategy as cds_sequence to reduce # of requests.
              seqs = []
              for start, end in self.exons:
                  seqs.append(_sequence(db, self.chrom, start + 1, end))
              return seqs
docs: Return the sequence for this feature.
          if per-exon is True, return an array of exon sequences
          This sequence is never reverse complemented