How to use the aniso8601.resolution.DateResolution.Day function in aniso8601

# 1) When split on a hyphen, the sizes of the parts are 4, 2, 2 or 4, 2
    # 2) There are no hyphens, and the length is 8
    datestrsplit = isodatestr.split('-')

    #Check case 1
    if len(datestrsplit) == 2:
        if len(datestrsplit[0]) == 4 and len(datestrsplit[1]) == 2:
            return DateResolution.Month

    if len(datestrsplit) == 3:
        if len(datestrsplit[0]) == 4 and len(datestrsplit[1]) == 2 and len(datestrsplit[2]) == 2:
            return DateResolution.Day

    #Check case 2
    if len(isodatestr) == 8 and isodatestr.find('-') == -1:
        return DateResolution.Day

    #An ISO string may be a ordinal date representation if:
    # 1) When split on a hyphen, the sizes of the parts are 4, 3
    # 2) There are no hyphens, and the length is 7

    #Check case 1
    if len(datestrsplit) == 2:
        if len(datestrsplit[0]) == 4 and len(datestrsplit[1]) == 3:
            return DateResolution.Ordinal

    #Check case 2
    if len(isodatestr) == 7 and isodatestr.find('-') == -1:
        return DateResolution.Ordinal

    #None of the date representations match
    raise ValueError('String is not an ISO 8601 date, perhaps it represents a time or datetime.')

#Stolen from:
    #http://stackoverflow.com/questions/304256/whats-the-best-way-to-find-the-inverse-of-datetime-isocalendar

    #Determine the location of the 4th of January, the first week of the ISO
    #year in the week containing the 4th of January
    #http://en.wikipedia.org/wiki/ISO_week_date
    fourth_jan = datetime.date(isoyear, 1, 4)

    #Note the conversion from ISO day (1 - 7) and Python day (0 - 6)
    delta = datetime.timedelta(fourth_jan.isoweekday() - 1)

    #Return the start of the year
    return fourth_jan - delta

_resolution_map = {
    DateResolution.Day: _parse_calendar_day,
    DateResolution.Ordinal: _parse_ordinal_date,
    DateResolution.Month: _parse_calendar_month,
    DateResolution.Week: _parse_week,
    DateResolution.Weekday: _parse_week_day,
    DateResolution.Year: _parse_year
}