'Parse command-line args and return options object.
returns: opts parse options dict'

def parseArgs(self):

    if ('--custom' in sys.argv):
        index = sys.argv.index('--custom')
        if (len(sys.argv) > (index + 1)):
            filename = sys.argv[(index + 1)]
            self.parseCustomFile(filename)
        else:
            raise Exception('Custom    file    name    not    found')
    desc = 'The    %prog    utility    creates    Mininet    network    from    the\ncommand    line.    It    can    create    parametrized    topologies,\ninvoke    the    Mininet    CLI,    and    run    tests.'
    usage = '%prog    [options]\n(type    %prog    -h    for    details)'
    opts = OptionParser(description=desc, usage=usage)
    addDictOption(opts, TOPOS, TOPODEF, 'topo')
    addDictOption(opts, LINKS, LINKDEF, 'link')
    opts.add_option('--custom', type='string', default=None, help=('read    custom    topo    and    node    params    from    .py' + 'file'))
    (self.options, self.args) = opts.parse_args()
    if self.args:
        opts.print_help()
        exit()
