How to use the rospkg.get_etc_ros_dir function in rospkg

def get_roscore_filename():
    # precedence: look for version in /etc/ros.  If it's not there, fall back to roslaunch package
    filename = os.path.join(rospkg.get_etc_ros_dir(), 'roscore.xml')
    if os.path.isfile(filename):
        return filename
    r = rospkg.RosPack()
    return os.path.join(r.get_path('roslaunch'), 'resources', 'roscore.xml')

# the log dir itself should not be symlinked as latest
    if logfile_dir != log_dir:
        if sys.platform not in ['win32']:
            try:
                success = renew_latest_logdir(logfile_dir)
                if not success:
                    sys.stderr.write("INFO: cannot create a symlink to latest log directory\n")
            except OSError as e:
                sys.stderr.write("INFO: cannot create a symlink to latest log directory: %s\n" % e)

    config_file = os.environ.get('ROS_PYTHON_LOG_CONFIG_FILE')
    if not config_file:
        # search for logging config file in ROS_HOME, ROS_ETC_DIR or relative
        # to the rosgraph package directory.
        config_dirs = [os.path.join(rospkg.get_ros_home(), 'config'),
                       rospkg.get_etc_ros_dir()]
        try:
            config_dirs.append(os.path.join(
                rospkg.RosPack().get_path('rosgraph'), 'conf'))
        except rospkg.common.ResourceNotFound:
            pass
        for config_dir in config_dirs:
            for extension in ('conf', 'yaml'):
                f = os.path.join(config_dir,
                                 'python_logging{}{}'.format(os.path.extsep,
                                                             extension))
                if os.path.isfile(f):
                    config_file = f
                    break
            if config_file is not None:
                break

def get_sources_list_dir():
    # base of where we read config files from
    # TODO: windows
    if 0:
        # we can't use etc/ros because environment config does not carry over under sudo
        etc_ros = rospkg.get_etc_ros_dir()
    else:
        etc_ros = '/etc/ros'
    # compute default system wide sources directory
    sys_sources_list_dir = os.path.join(etc_ros, 'rosdep', SOURCES_LIST_DIR)
    sources_list_dirs = get_sources_list_dirs(sys_sources_list_dir)
    if sources_list_dirs:
        return sources_list_dirs[0]
    else:
        return sys_sources_list_dir