def get_weekday_number(str_weekday):
    """
    Using name of weekday return its number representation
    :param str_weekday: weekday from mon - sun
    :return: integer number [0..7]
    """
    weekdays = (
        'mon',
        'tue',
        'wed',
        'thu',
        'fri',
        'sat',
        'sun'
    )
    return weekdays.index(str_weekday[:3].lower())