code: def acgtn_only(infile, outfile):
      '''Replace every non-acgtn (case insensitve) character with an N'''
      f = utils.open_file_write(outfile)
      for seq in sequences.file_reader(infile):
          seq.replace_non_acgt()
          print(seq, file=f)
      utils.close(ff acgtn_only(infile, outfile):
      '''Replace every non-acgtn (case insensitve) character with an N'''
      f = utils.open_file_write(outfile)
      for seq in sequences.file_reader(infile):
          seq.replace_non_acgt()
          print(seq, file=f)
      utils.close(f)
docs: Replace every non-acgtn (case insensitve) character with an N