def get_log_fpath(num='next', appname=None, log_dir=None):
    """
    Returns:
        log_fpath (str): path to log file
    """
    if log_dir is None:
        log_dir = get_logging_dir(appname=appname)
    if not exists(log_dir):
        os.makedirs(log_dir)
    if appname is not None:
        log_fname = appname + '_logs_%04d.out'
    else:
        log_fname = 'utool_logs_%04d.out'
    if isinstance(num, six.string_types):
        if num == 'next':
            count = 0
            log_fpath = join(log_dir, log_fname % count)
            while exists(log_fpath):
                log_fpath = join(log_dir, log_fname % count)
                count += 1
    else:
        log_fpath = join(log_dir, log_fname % num)
    return log_fpath
Returns:
        log_fpath (str): path to log file