'Return a model data element'

def data(self, index, role=Qt.DisplayRole):

    if (not index.isValid()):
        return to_qvariant()
    if (role == Qt.DisplayRole):
        return self._display_data(index)
    elif (role == Qt.BackgroundColorRole):
        return to_qvariant(get_color(self._data[index.row()][index.column()], 0.2))
    elif (role == Qt.TextAlignmentRole):
        return to_qvariant(int((Qt.AlignRight | Qt.AlignVCenter)))
    return to_qvariant()
