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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 pull(args):
 """ %prog pull version partID unitigID For example, `%prog pull 5 530` will pull the utg530 from partition 5 The layout is written to `unitig530` """

    p = OptionParser(pull.__doc__)
    opts, args = p.parse_args(args)

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

    prefix = get_prefix()
    version, partID, unitigID = args
    s = ".".join(args)

    cmd = "tigStore"
    cmd += " -g ../{0}.gkpStore -t ../{0}.tigStore".format(prefix)
    cmd += " {0} -up {1} -d layout -u {2}".format(version, partID, unitigID)

    unitigfile = "unitig" + s
    sh(cmd, outfile=unitigfile)

    return unitigfile