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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 main(argv=None):
 """Main entry point for the cdstar CLI."""

    args = docopt(__doc__, version=pycdstar.__version__, argv=argv, options_first=True)
    subargs = [args['<command>']] + args['<args>']

    if args['<command>'] in ['help', None]:
        cmd = None
        if len(subargs) > 1:
            cmd = COMMANDS.get(subargs[1])
        if cmd:
            print(cmd.__doc__)
        else:
            print(__doc__)
        return 0

    cmd = COMMANDS.get(args['<command>'])
    if not cmd:
        print('unknown command')
        print(__doc__)
        return 0

    cfg = Config(**dict(
        cfg=args.pop('--cfg', None),
        url=args.pop('--service', None),
        user=args.pop('--user', None),
        password=args.pop('--password', None)))

    try:
        res = cmd(
            Cdstar(cfg=cfg),
            docopt(cmd.__doc__, argv=subargs),
            verbose=args.get('--verbose'))
        if isinstance(res, types.GeneratorType):
            res = list(res)
        if isinstance(res, list):
            for line in res:
                print(line)
            res = 0
        return res or 0
    except:  # noqa: E722; # pragma: no cover
        # FIXME: log exception!
        return 256