'Set header data'

def headerData(self, section, orientation, role=Qt.DisplayRole):

    if (role != Qt.DisplayRole):
        return to_qvariant()
    labels = (self.xlabels if (orientation == Qt.Horizontal) else self.ylabels)
    if (labels is None):
        return to_qvariant(int(section))
    else:
        return to_qvariant(labels[section])
