def METHOD_NAME(self, number, format=None):
    """Returns the msgid which can be passed to the translation service
    for l10n of weekday names. Format is either None, 'a' or 's'.
    >>> ttool = TranslationServiceTool()
    >>> ttool.day_msgid(0)
    'weekday_sun'
    >>> ttool.day_msgid(6)
    'weekday_sat'
    >>> ttool.day_msgid(0, format='a')
    'weekday_sun_abbr'
    >>> ttool.day_msgid(3, format='s')
    'weekday_wed_short'
    """
    #
    if format == "s":
        # short format
        method = weekdayname_msgid_short
    elif format == "a":
        # abbreviation
        method = weekdayname_msgid_abbr
    else:
        # long format
        method = weekdayname_msgid
    return method(number)