code: def get_sequence(self,ref):
      
      strand = '+'
      if not self._options.direction:
        sys.stderr.write("WARNING: no strand information for the transcript\n")
      if self._options.direction: strand = self._options.direction
      seq = ''
      for e in [x.range for x in self.exons]:
        seq += str(ref[e.chr][e.start-1:e.end])
      if strand == '-':  seq = rc(seq)
      return Sequence(seq.upper())
docs: get a sequence given a reference