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

week_date_len = 7 + hyphens_present
        weekday_date_len = 8 + 2*hyphens_present
        if isodatestrlen == week_date_len:
            #YYYY-Www
            #YYYYWww
            return DateResolution.Week
        elif isodatestrlen == weekday_date_len:
            #YYYY-Www-D
            #YYYYWwwD
            return DateResolution.Weekday
        else:
            raise ValueError('String is not a valid ISO 8601 week date.')

    #If the size of the string of 4 or less, assume its a truncated year representation
    if len(isodatestr) <= 4:
        return DateResolution.Year

    #An ISO string may be a calendar represntation if:
    # 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

#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
}