code: def print_single(line, rev):
      
      if rev is True:
          seq = rc(['', line[9]])[1]
          qual = line[10][::-1]
      else:
          seq = line[9]
          qual = line[10]
      fq = ['@%s' % line[0], seq, '+%s' % line[0], qual]
      print('\n'.join(fq), file = sys.stderr)
docs: print single reads to stderr