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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 cli():
 """Command line utility for serving datasets in a directory over HTTP."""

    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        "dataset_directory",
        help="Directory with datasets to be served"
    )
    parser.add_argument(
        "-p",
        "--port",
        type=int,
        default=8081,
        help="Port to serve datasets on (default 8081)"
    )
    args = parser.parse_args()
    if not os.path.isdir(args.dataset_directory):
        parser.error("Not a directory: {}".format(args.dataset_directory))

    serve_dtool_directory(args.dataset_directory, args.port)