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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def set_identifiertext(self, index):
 """Set the identifier text on the identifier_lb :param index: the index :type index: :class:`QtGui.QModelIndex` :returns: None :rtype: None :raises: None """

        dr = QtCore.Qt.DisplayRole
        t = index.model().index(index.row(), 17, index.parent()).data(dr)
        if t is None:
            t = -1
        else:
            t = t+1
        self.identifier_lb.setText("#%s" % t)