def METHOD_NAME(readwrite, filename, duration):
    """Return standardized I/O timing message string for logging
    Args:
        readwrite (str): either "read" or "write"
        filename (str): filename that was read or written
        duration (float): time in seconds to perform I/O operations
    Returns: I/O timing message to log
    Note: this function does not call log.info() itself so that the logging
    source file and line number can be associated with the I/O function itself
    instead of this utility formatting function.
    """
    basename = os.path.basename(filename)
    timestamp = datetime.datetime.now().isoformat()
    msg = f"iotime {duration:.3f} sec to {readwrite} {basename} at {timestamp}"
    return msg