code: def map_to_precursors_on_fly(seqs, names, loci, args):
      
      precursor = precursor_sequence(loci, args.ref).upper()
      dat = dict()
      for s, n in itertools.izip(seqs, names):
          res = pyMatch.Match(precursor, str(s), 1, 3)
          if res > -1:
              dat[n] = [res, res + len(s)]
      logger.debug("mapped in %s: %s out of %s" % (loci, len(dat), len(seqs)))
      return dat
docs: map sequences to precursors with franpr algorithm to avoid writting on disk