Parse the arguments/options passed to the program on the command line.

def parse_args(args=None):
    """
    Parse the arguments/options passed to the program on the command line.
    """

    parse_kwargs = {
        "description":  'Download Coursera.org lecture material and resources.'
    }

    conf_file_path = os.path.join(os.getcwd(), LOCAL_CONF_FILE_NAME)
    if os.path.isfile(conf_file_path):
        parse_kwargs["default_config_files"] = [conf_file_path]
    parser = argparse.ArgParser(**parse_kwargs)

    # Basic options
    group_basic = parser.add_argument_group('Basic options')

    group_basic.add_argument(
        'class_names',
        action='store',
        nargs='*',
        help='name(s) of the class(es) (e.g. "ml-005")')

    group_basic.add_argument(
        '-u',
        '--username',
        dest='username',
        action='store',
        default=None,
        help='username (email) that you use to login to Coursera')

    group_basic.add_argument(
        '-p',
        '--password',
        dest='password',
        action='store',
        default=None,
        help='coursera password')

    group_basic.add_argument(
        '--jobs',
        dest='jobs',
        action='store',
        default=1,
        type=int,
        help='number of parallel jobs to use for '
        'downloading resources. (Default: 1)')

    group_basic.add_argument(
        '--download-delay',
        dest='download_delay',
        action='store',
        default=60,
        type=int,
        help='number of seconds to wait before downloading '
        'next course. (Default: 60)')

    group_basic.add_argument(
        '-b',  # FIXME: kill this one-letter option
        '--preview',
        dest='preview',
        action='store_true',
        default=False,
        help='get videos from preview pages. (Default: False)')

    group_basic.add_argument(
        '--path',
        dest='path',
        action='store',
        default='',
        help='path to where to save the file. (Default: current directory)')

    group_basic.add_argument(
        '-sl',  # FIXME: deprecate this option
        '--subtitle-language',
        dest='subtitle_language',
        action='store',
        default='all',
        help='Choose language to download subtitles and transcripts.'
        '(Default: all) Use special value "all" to download all available.'
        'To download subtitles and transcripts of multiple languages,'
        'use comma(s) (without spaces) to seperate the names of the languages,'
        ' i.e., "en,zh-CN".'
        'To download subtitles and transcripts of alternative language(s) '
        'if only the current language is not available,'
        'put an "|<lang>" for each of the alternative languages after '
        'the current language, i.e., "en|fr,zh-CN|zh-TW|de", and make sure '
        'the parameter are wrapped with quotes when "|" presents.'

    )

    # Selection of material to download
    group_material = parser.add_argument_group(
        'Selection of material to download')

    group_material.add_argument(
        '--specialization',
        dest='specialization',
        action='store_true',
        default=False,
        help='treat given class names as specialization names and try to '
        'download its courses, if available. Note that there are name '
        'clashes, e.g. "machine-learning" is both a course and a '
        'specialization (Default: False)')

    group_material.add_argument(
        '--only-syllabus',
        dest='only_syllabus',
        action='store_true',
        default=False,
        help='download only syllabus, skip course content. '
        '(Default: False)')

    group_material.add_argument(
        '--download-quizzes',
        dest='download_quizzes',
        action='store_true',
        default=False,
        help='download quiz and exam questions. (Default: False)')

    group_material.add_argument(
        '--download-notebooks',
        dest='download_notebooks',
        action='store_true',
        default=False,
        help='download Python Jupyther Notebooks. (Default: False)')

    group_material.add_argument(
        '--about',  # FIXME: should be --about-course
        dest='about',
        action='store_true',
        default=False,
        help='download "about" metadata. (Default: False)')

    group_material.add_argument(
        '-f',
        '--formats',
        dest='file_formats',
        action='store',
        default='all',
        help='file format extensions to be downloaded in'
        ' quotes space separated, e.g. "mp4 pdf" '
        '(default: special value "all")')

    group_material.add_argument(
        '--ignore-formats',
        dest='ignore_formats',
        action='store',
        default=None,
        help='file format extensions of resources to ignore'
        ' (default: None)')

    group_material.add_argument(
        '-sf',  # FIXME: deprecate this option
        '--section_filter',
        dest='section_filter',
        action='store',
        default=None,
        help='only download sections which contain this'
        ' regex (default: disabled)')

    group_material.add_argument(
        '-lf',  # FIXME: deprecate this option
        '--lecture_filter',
        dest='lecture_filter',
        action='store',
        default=None,
        help='only download lectures which contain this regex'
        ' (default: disabled)')

    group_material.add_argument(
        '-rf',  # FIXME: deprecate this option
        '--resource_filter',
        dest='resource_filter',
        action='store',
        default=None,
        help='only download resources which match this regex'
        ' (default: disabled)')

    group_material.add_argument(
        '--video-resolution',
        dest='video_resolution',
        action='store',
        default='540p',
        help='video resolution to download (default: 540p); '
        'only valid for on-demand courses; '
        'only values allowed: 360p, 540p, 720p')

    group_material.add_argument(
        '--disable-url-skipping',
        dest='disable_url_skipping',
        action='store_true',
        default=False,
        help='disable URL skipping, all URLs will be '
        'downloaded (default: False)')

    # Parameters related to external downloaders
    group_external_dl = parser.add_argument_group('External downloaders')

    group_external_dl.add_argument(
        '--wget',
        dest='wget',
        action='store',
        nargs='?',
        const='wget',
        default=None,
        help='use wget for downloading,'
        'optionally specify wget bin')

    group_external_dl.add_argument(
        '--curl',
        dest='curl',
        action='store',
        nargs='?',
        const='curl',
        default=None,
        help='use curl for downloading,'
        ' optionally specify curl bin')

    group_external_dl.add_argument(
        '--aria2',
        dest='aria2',
        action='store',
        nargs='?',
        const='aria2c',
        default=None,
        help='use aria2 for downloading,'
        ' optionally specify aria2 bin')

    group_external_dl.add_argument(
        '--axel',
        dest='axel',
        action='store',
        nargs='?',
        const='axel',
        default=None,
        help='use axel for downloading,'
        ' optionally specify axel bin')

    group_external_dl.add_argument(
        '--downloader-arguments',
        dest='downloader_arguments',
        default='',
        help='additional arguments passed to the'
        ' downloader')

    parser.add_argument(
        '--list-courses',
        dest='list_courses',
        action='store_true',
        default=False,
        help='list course names (slugs) and quit. Listed '
        'course names can be put into program arguments')

    parser.add_argument(
        '--resume',
        dest='resume',
        action='store_true',
        default=False,
        help='resume incomplete downloads (default: False)')

    parser.add_argument(
        '-o',
        '--overwrite',
        dest='overwrite',
        action='store_true',
        default=False,
        help='whether existing files should be overwritten'
        ' (default: False)')

    parser.add_argument(
        '--verbose-dirs',
        dest='verbose_dirs',
        action='store_true',
        default=False,
        help='include class name in section directory name')

    parser.add_argument(
        '--quiet',
        dest='quiet',
        action='store_true',
        default=False,
        help='omit as many messages as possible'
        ' (only printing errors)')

    parser.add_argument(
        '-r',
        '--reverse',
        dest='reverse',
        action='store_true',
        default=False,
        help='download sections in reverse order')

    parser.add_argument(
        '--combined-section-lectures-nums',
        dest='combined_section_lectures_nums',
        action='store_true',
        default=False,
        help='include lecture and section name in final files')

    parser.add_argument(
        '--unrestricted-filenames',
        dest='unrestricted_filenames',
        action='store_true',
        default=False,
        help='Do not limit filenames to be ASCII-only')

    # Advanced authentication
    group_adv_auth = parser.add_argument_group(
        'Advanced authentication options')

    group_adv_auth.add_argument(
        '-c',
        '--cookies_file',
        dest='cookies_file',
        action='store',
        default=None,
        help='full path to the cookies.txt file')

    group_adv_auth.add_argument(
        '-n',
        '--netrc',
        dest='netrc',
        nargs='?',
        action='store',
        const=True,
        default=False,
        help='use netrc for reading passwords, uses default'
        ' location if no path specified')

    group_adv_auth.add_argument(
        '-k',
        '--keyring',
        dest='use_keyring',
        action='store_true',
        default=False,
        help='use keyring provided by operating system to '
        'save and load credentials')

    group_adv_auth.add_argument(
        '--clear-cache',
        dest='clear_cache',
        action='store_true',
        default=False,
        help='clear cached cookies')

    # Advanced miscellaneous options
    group_adv_misc = parser.add_argument_group(
        'Advanced miscellaneous options')

    group_adv_misc.add_argument(
        '--hook',
        dest='hooks',
        action='append',
        default=[],
        help='hooks to run when finished')

    group_adv_misc.add_argument(
        '-pl',
        '--playlist',
        dest='playlist',
        action='store_true',
        default=False,
        help='generate M3U playlists for course weeks')

    group_adv_misc.add_argument(
        '--mathjax-cdn',
        dest='mathjax_cdn_url',
        default='https://cdn.mathjax.org/mathjax/latest/MathJax.js',
        help='the cdn address of MathJax.js'
    )

    # Debug options
    group_debug = parser.add_argument_group('Debugging options')

    group_debug.add_argument(
        '--skip-download',
        dest='skip_download',
        action='store_true',
        default=False,
        help='for debugging: skip actual downloading of files')

    group_debug.add_argument(
        '--debug',
        dest='debug',
        action='store_true',
        default=False,
        help='print lots of debug information')

    group_debug.add_argument(
        '--cache-syllabus',
        dest='cache_syllabus',
        action='store_true',
        default=False,
        help='cache course syllabus into a file')

    group_debug.add_argument(
        '--version',
        dest='version',
        action='store_true',
        default=False,
        help='display version and exit')

    group_debug.add_argument(
        '-l',  # FIXME: remove short option from rarely used ones
        '--process_local_page',
        dest='local_page',
        help='uses or creates local cached version of syllabus'
        ' page')

    # Final parsing of the options
    args = parser.parse_args(args)

    # Initialize the logging system first so that other functions
    # can use it right away
    if args.debug:
        logging.basicConfig(level=logging.DEBUG,
                            format='%(name)s[%(funcName)s] %(message)s')
    elif args.quiet:
        logging.basicConfig(level=logging.ERROR,
                            format='%(name)s: %(message)s')
    else:
        logging.basicConfig(level=logging.INFO,
                            format='%(message)s')

    if class_name_arg_required(args) and not args.class_names:
        parser.print_usage()
        logging.error('You must supply at least one class name')
        sys.exit(1)

    # show version?
    if args.version:
        # we use print (not logging) function because version may be used
        # by some external script while logging may output excessive
        # information
        print(__version__)
        sys.exit(0)

    # turn list of strings into list
    args.downloader_arguments = args.downloader_arguments.split()

    # turn list of strings into list
    args.file_formats = args.file_formats.split()

    # decode path so we can work properly with cyrillic symbols on different
    # versions on Python
    args.path = decode_input(args.path)

    # check arguments
    if args.use_keyring and args.password:
        logging.warning(
            '--keyring and --password cannot be specified together')
        args.use_keyring = False

    if args.use_keyring and not keyring:
        logging.warning('The python module `keyring` not found.')
        args.use_keyring = False

    if args.cookies_file and not os.path.exists(args.cookies_file):
        logging.error('Cookies file not found: %s', args.cookies_file)
        sys.exit(1)

    if not args.cookies_file:
        try:
            args.username, args.password = get_credentials(
                username=args.username, password=args.password,
                netrc=args.netrc, use_keyring=args.use_keyring)
        except CredentialsError as e:
            logging.error(e)
            sys.exit(1)

    return args