<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def needle(args):
 """ %prog needle nw.pairs a.pep.fasta b.pep.fasta Take protein pairs and needle them Automatically writes output file `nw.scores` """

    from jcvi.formats.fasta import Fasta, SeqIO

    p = OptionParser(needle.__doc__)

    opts, args = p.parse_args(args)

    if len(args) != 3:
        sys.exit(not p.print_help())

    manager = mp.Manager()
    results = manager.list()
    needle_pool = mp.Pool(processes=mp.cpu_count())

    pairsfile, apep, bpep = args
    afasta, bfasta = Fasta(apep), Fasta(bpep)
    fp = must_open(pairsfile)
    for i, row in enumerate(fp):
        a, b = row.split()
        a, b = afasta[a], bfasta[b]
        fa, fb = must_open("{0}_{1}_a.fasta".format(pairsfile, i), "w"), \
            must_open("{0}_{1}_b.fasta".format(pairsfile, i), "w")
        SeqIO.write([a], fa, "fasta")
        SeqIO.write([b], fb, "fasta")
        fa.close()
        fb.close()

        needlefile = "{0}_{1}_ab.needle".format(pairsfile, i)
        needle_pool.apply_async(_needle, \
            (fa.name, fb.name, needlefile, a.id, b.id, results))

    needle_pool.close()
    needle_pool.join()

    fp.close()

    scoresfile = "{0}.scores".format(pairsfile.rsplit(".")[0])
    fw = must_open(scoresfile, "w")
    for result in results:
        print(result, file=fw)
    fw.close()