def add_logging_handler(handler, format_='file'):
    """
    mostly for util_logging internals
    """
    global __UTOOL_ROOT_LOGGER__
    if __UTOOL_ROOT_LOGGER__ is None:
        builtins.print('[WARNING] logger not started, cannot add handler')
        return
    # create formatter and add it to the handlers
    #logformat = '%Y-%m-%d %H:%M:%S'
    #logformat = '%(asctime)s - %(name)s - %(levelname)s - %(message)s'
    timeformat = '%H:%M:%S'
    if format_ == 'file':
        logformat = '[%(asctime)s]%(message)s'
    elif format_ == 'stdout':
        logformat = '%(message)s'
    else:
        raise AssertionError('unknown logging format_: %r' % format_)
    # Create formatter for handlers
    formatter = logging.Formatter(logformat, timeformat)
    handler.setLevel(logging.DEBUG)
    handler.setFormatter(formatter)
    __UTOOL_ROOT_LOGGER__.addHandler(handler)