problem with enumeration is soapfish

gistfile1.txt

class ListaPreCasd(xsd.ComplexType):
    INHERITANCE = None
    INDICATOR = xsd.Sequence
    CuaaForn = xsd.Element(CUAA)
    CodiRegiForn = xsd.Element(TipoCodice)
    CodiceAllegato = xsd.Element(TipoCodice, minOccurs=0)
    CodiceVino = xsd.Element(TipoCodiceDopIgp, minOccurs=0)
    QuantitaUva = xsd.Element(QtaKgCarico)
    CodiceColore = xsd.Element(xsd.String(enumeration=['B', 'N']length=1,))
    AnnoCampagna = xsd.Element(TipoAnno)
    CuaaDest = xsd.Element(CUAA)
    CodiRegiDest = xsd.Element(TipoCodice)
    CodIcqrf = xsd.Element(CodiceIcq)
    DataInvi = xsd.Element(xsd.Date)
    DataBloc = xsd.Element(xsd.Date)
    DataAgg = xsd.Element(xsd.Date)
    CodClassificazione = xsd.Element(TipoCodice, minOccurs=0)
    CodCategoria = xsd.Element(TipoCodice)

    @classmethod
    def create(cls, CuaaForn, CodiRegiForn, QuantitaUva, CodiceColore, AnnoCampagna, CuaaDest, CodiRegiDest, CodIcqrf, DataInvi, DataBloc, DataAgg, CodCategoria):
        instance = cls()
        instance.CuaaForn = CuaaForn
        instance.CodiRegiForn = CodiRegiForn
        instance.QuantitaUva = QuantitaUva
        instance.CodiceColore = CodiceColore
        instance.AnnoCampagna = AnnoCampagna
        instance.CuaaDest = CuaaDest
        instance.CodiRegiDest = CodiRegiDest
        instance.CodIcqrf = CodIcqrf
        instance.DataInvi = DataInvi
        instance.DataBloc = DataBloc
        instance.DataAgg = DataAgg
        instance.CodCategoria = CodCategoria
        return instance