def STR_LEN_BYTES(expression):
    """
    Returns the number of UTF-8 encoded bytes in the specified string.
    https://docs.mongodb.com/manual/reference/operator/aggregation/strLenBytes/
    for more details
    :param expression: The string or expression of the string
    :return: Aggregation operator
    """
    return {'$strLenBytes': expression}
