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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 _download_mirbase(args, version="CURRENT"):
 """ Download files from mirbase """

    if not args.hairpin or not args.mirna:
        logger.info("Working with version %s" % version)
        hairpin_fn = op.join(op.abspath(args.out), "hairpin.fa.gz")
        mirna_fn = op.join(op.abspath(args.out), "miRNA.str.gz")
        if not file_exists(hairpin_fn):
            cmd_h = "wget ftp://mirbase.org/pub/mirbase/%s/hairpin.fa.gz -O %s &&  gunzip -f !$" % (version, hairpin_fn)
            do.run(cmd_h, "download hairpin")
        if not file_exists(mirna_fn):
            cmd_m = "wget ftp://mirbase.org/pub/mirbase/%s/miRNA.str.gz -O %s && gunzip -f !$" % (version, mirna_fn)
            do.run(cmd_m, "download mirna")
    else:
        return args.hairpin, args.mirna