def __getitem__(self, idx):
        r"""Get graph by index

        Parameters
        ----------
        idx : int
            Item index

        Returns
        -------
        :class:`dgl.DGLGraph`

            The graph contains:

            - ``ndata['feat']``: node features
            - ``ndata['label']``: node labels
        """
        assert idx == 0, "This dataset has only one graph"
        if self._transform is None:
            return self._graph
        else:
            return self._transform(self._graph)
Get graph by index

        Parameters
        ----------
        idx : int
            Item index

        Returns
        -------
        :class:`dgl.DGLGraph`

            The graph contains:

            - ``ndata['feat']``: node features
            - ``ndata['label']``: node labels
        
python/dgl/data/gnn_benchmark.py