def setup_logger(name="ppdet", output=None, log_ranks="0"):
    """
    Initialize logger and set its verbosity level to INFO.
    Args:
        output (str): a file name or a directory to save log. If None, will not save log file.
            If ends with ".txt" or ".log", assumed to be a file name.
            Otherwise, logs will be saved to `output/log.txt`.
        name (str): the root module name of this logger
        log_ranks (str): The ids of gpu to log which are separated by "," when more than 1, "0" by default.

    Returns:
        logging.Logger: a logger
    """
    logger = logging.getLogger(name)
    if name in logger_initialized:
        return logger

    logger.setLevel(logging.INFO)
    logger.propagate = False

    formatter = logging.Formatter(
        "[%(asctime)s] %(name)s %(levelname)s: %(message)s",
        datefmt="%m/%d %H:%M:%S")
    
    if isinstance(log_ranks, str):
        log_ranks = [int(i) for i in log_ranks.split(',')]
    elif isinstance(log_ranks, int):
        log_ranks = [log_ranks]

    # stdout logging: master only
    local_rank = dist.get_rank()
    if local_rank in log_ranks:
        ch = logging.StreamHandler(stream=sys.stdout)
        ch.setLevel(logging.DEBUG)
        ch.setFormatter(formatter)
        logger.addHandler(ch)

    # file logging: all workers
    if output is not None:
        if output.endswith(".txt") or output.endswith(".log"):
            filename = output
        else:
            filename = os.path.join(output, "log.txt")
        if local_rank > 0:
            filename = filename + ".rank{}".format(local_rank)
        os.makedirs(os.path.dirname(filename))
        fh = logging.FileHandler(filename, mode='a')
        fh.setLevel(logging.DEBUG)
        fh.setFormatter(logging.Formatter())
        logger.addHandler(fh)

    logger_initialized.append(name)
    return logger

    Initialize logger and set its verbosity level to INFO.
    Args:
        output (str): a file name or a directory to save log. If None, will not save log file.
            If ends with ".txt" or ".log", assumed to be a file name.
            Otherwise, logs will be saved to `output/log.txt`.
        name (str): the root module name of this logger
        log_ranks (str): The ids of gpu to log which are separated by "," when more than 1, "0" by default.

    Returns:
        logging.Logger: a logger
    
ppdet/utils/logger.py