How to use the mozregression.config.DEFAULT_CONF_FNAME function in mozregression

def __call__(self, parser, namespace, values, option_string=None):
        write_config(DEFAULT_CONF_FNAME)
        parser.exit()

def save_prefs(options):
    conf_dir = os.path.dirname(DEFAULT_CONF_FNAME)
    if not os.path.isdir(conf_dir):
        os.makedirs(conf_dir)

    settings = ConfigObj(DEFAULT_CONF_FNAME)
    settings.update(
        {
            "persist": options["persist"] or "",
            "http-timeout": options["http_timeout"],
            "persist-size-limit": options["persist_size_limit"],
            "background_downloads": "yes" if options["background_downloads"] else "no",
            "approx-policy": "auto" if options["approx_policy"] else "none",
            "enable-telemetry": "yes" if options["enable_telemetry"] else "no",
        }
    )
    # only save base url in the file if it differs from the default.
    if options["archive_base_url"] and options["archive_base_url"] != ARCHIVE_BASE_URL:
        settings["archive-base-url"] = options["archive_base_url"]
    elif "archive-base-url" in settings:
        del settings["archive-base-url"]
    # likewise only save args if it has a value

def set_default_prefs():
    """Set the default prefs for a first launch of the application."""
    if not os.path.isfile(DEFAULT_CONF_FNAME):
        options = get_prefs()
        options["persist"] = os.path.join(os.path.dirname(DEFAULT_CONF_FNAME), "persist")
        options["persist_size_limit"] = 2.0
        save_prefs(options)

def cli(argv=None, conf_file=DEFAULT_CONF_FNAME, namespace=None):
    """
    parse cli args basically and returns a :class:`Configuration`.

    if namespace is given, it will be used as a arg parsing result, so no
    arg parsing will be done.
    """
    config = get_config(conf_file)
    if namespace:
        options = namespace
    else:
        options = parse_args(argv=argv, defaults=config)
        if not options.cmdargs:
            # we don't set the cmdargs default to be that from the
            # configuration file, because then any new arguments
            # will be appended: https://bugs.python.org/issue16399
            options.cmdargs = config["cmdargs"]

try:
        # else, try to load a valid certificate locally
        with open(TC_CREDENTIALS_FNAME) as f:
            creds = json.load(f)
        if not tc_utils.isExpired(creds["certificate"]):
            return creds
    except Exception:
        pass

    # here we need to ask for a certificate, this require web browser
    # authentication
    logger.info(
        "Authentication required from taskcluster. We are going to ask for a"
        " certificate.\nNote that if you have long term access you can instead"
        " set your taskcluster-clientid and taskcluster-accesstoken in the"
        " configuration file (%s)." % DEFAULT_CONF_FNAME
    )
    creds = tc_utils.authenticate("mozregression private build access")

    # save the credentials and the certificate for later use
    with open(TC_CREDENTIALS_FNAME, "w") as f:
        json.dump(creds, f)
    return creds

def save_prefs(options):
    conf_dir = os.path.dirname(DEFAULT_CONF_FNAME)
    if not os.path.isdir(conf_dir):
        os.makedirs(conf_dir)

    settings = ConfigObj(DEFAULT_CONF_FNAME)
    settings.update(
        {
            "persist": options["persist"] or "",
            "http-timeout": options["http_timeout"],
            "persist-size-limit": options["persist_size_limit"],
            "background_downloads": "yes" if options["background_downloads"] else "no",
            "approx-policy": "auto" if options["approx_policy"] else "none",
            "enable-telemetry": "yes" if options["enable_telemetry"] else "no",
        }
    )
    # only save base url in the file if it differs from the default.
    if options["archive_base_url"] and options["archive_base_url"] != ARCHIVE_BASE_URL: