def acgtn_only(infile, outfile):
f = utils.open_file_write(outfile)<EOL>for seq in sequences.file_reader(infile):<EOL><INDENT>seq.replace_non_acgt()<EOL>print(seq, file=f)<EOL><DEDENT>utils.close(f)<EOL>
Replace every non-acgtn (case insensitve) character with an N