Initialize a logger

    Parameters
    ----------
    root_dir : str
        directory for saving log
    name : str
        name of logger

    Returns
    -------
    logger : logging.Logger
        a logger

def init_logger(root_dir, name="train.log"):
    """Initialize a logger

    Parameters
    ----------
    root_dir : str
        directory for saving log
    name : str
        name of logger

    Returns
    -------
    logger : logging.Logger
        a logger
    """
    os.makedirs(root_dir, exist_ok=True)
    log_formatter = logging.Formatter("%(message)s")
    logger = logging.getLogger(name)
    file_handler = logging.FileHandler("{0}/{1}".format(root_dir, name), mode='w')
    file_handler.setFormatter(log_formatter)
    logger.addHandler(file_handler)
    console_handler = logging.StreamHandler()
    console_handler.setFormatter(log_formatter)
    logger.addHandler(console_handler)
    logger.setLevel(logging.INFO)
    return logger