def ISO_DAY_OF_WEEK(expression):
    """
    Returns the weekday number in ISO 8601 format, ranging from 1 (for Monday) to 7 (for Sunday).
    See https://docs.mongodb.com/manual/reference/operator/aggregation/isoDayOfWeek/
    for more details
    :param expression: expression or variable of a Date, a Timestamp, or an ObjectID
    :return: Aggregation operator
    """
    return {'$isoDayOfWeek': expression}
