def METHOD_NAME(directory):
    """Download, unzip, clean and compress all data files.
    Accesses UN WPP data portal, downloads all necessary files (see `URLS`), and creates a zip folder with all of them
    named 'un_wpp.zip'
    """
    output_zip = "un_wpp"
    download_data(directory)
    unzip_data(directory)
    clean_directory(directory)
    output_file = compress_directory(directory, output_zip)
    return output_file