Creates an index. An item must exist for the given *row* 
        and *col*

        :returns: :qtdoc:`QModelIndex`

def index(self, row, col, parent=QtCore.QModelIndex()):
        """Creates an index. An item must exist for the given *row* 
        and *col*

        :returns: :qtdoc:`QModelIndex`
        """ 
        if row < self._stim.rowCount() and col < self._stim.columnCountForRow(row):
            component = self._stim.component(row, col)
            return self.createIndex(row, col, component)
        else:
            return QtCore.QModelIndex()