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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fasta(args):
 """ %prog fasta fastqfiles Convert fastq to fasta and qual file. """

    p = OptionParser(fasta.__doc__)
    p.add_option("--seqtk", default=False, action="store_true",
                 help="Use seqtk to convert")
    p.set_outdir()
    p.set_outfile(outfile=None)
    opts, args = p.parse_args(args)

    if len(args) < 1:
        sys.exit(not p.print_help())

    fastqfiles = args
    outdir = opts.outdir
    if outdir and outdir != ".":
        mkdir(outdir)

    fastqfile = fastqfiles[0]
    pf = op.basename(fastqfile)
    gzinput = pf.endswith(".gz")
    if gzinput:
        pf = pf.rsplit(".", 1)[0]

    pf, sf = pf.rsplit(".", 1)
    if sf not in ("fq", "fastq"):
        logging.debug("Assumed FASTA: suffix not `fq` or `fastq`")
        return fastqfile, None

    fastafile, qualfile = pf + ".fasta", pf + ".qual"
    outfile = opts.outfile or fastafile
    outfile = op.join(outdir, outfile)
    if opts.seqtk:
        if need_update(fastqfiles, outfile):
            for i, fastqfile in enumerate(fastqfiles):
                cmd = "seqtk seq -A {0} -L 30 -l 70".format(fastqfile)
                # First one creates file, following ones append to it
                sh(cmd, outfile=outfile, append=i)
        else:
            logging.debug("Outfile `{0}` already exists.".format(outfile))
        return outfile, None

    for fastqfile in fastqfiles:
        SeqIO.convert(fastqfile, "fastq", fastafile, "fasta")
        SeqIO.convert(fastqfile, "fastq", qualfile, "qual")

    return fastafile, qualfile