[BUGFIX] extand DGLGraph graph_data. (#632)

* enable tutorial test in CI.

* extand DGLGraph graph_data.

* update doc.

* Revert "enable tutorial test in CI."

This reverts commit cd774067180922bb6ae979bde4aecbffc61c8147.

* accept DGLGraph in graph store.

examples/mxnet/sampling/train.py

@@ -52,7 +52,7 @@ def main(args):
               n_test_samples))
 
     # create GCN model
-    g = data.graph
+    g = dgl.DGLGraph(data.graph, readonly=True)
     g.ndata['features'] = features
     g.ndata['labels'] = labels
 

python/dgl/contrib/graph_store.py

@@ -292,10 +292,19 @@ class SharedMemoryStoreServer(object):
     and store them in shared memory. The loaded graph can be identified by
     the graph name in the input argument.
 
+    DGL graph accepts graph data of multiple formats:
+
+    * NetworkX graph,
+    * scipy matrix,
+    * DGLGraph.
+
+    If the input graph data is DGLGraph, the constructed DGLGraph only contains
+    its graph index.
+
     Parameters
     ----------
     graph_data : graph data
-        Data to initialize graph. Same as networkx's semantics.
+        Data to initialize graph.
     edge_dir : string
         the edge direction for the graph structure ("in" or "out")
     graph_name : string
@@ -309,14 +318,14 @@ class SharedMemoryStoreServer(object):
     """
     def __init__(self, graph_data, edge_dir, graph_name, multigraph, num_workers, port):
         self.server = None
-        if isinstance(graph_data, GraphIndex):
-            graph_idx = graph_data
+        if isinstance(graph_data, (GraphIndex, DGLGraph)):
+            self._graph = DGLGraph(graph_data, multigraph=multigraph, readonly=True)
         else:
             indptr, indices = _to_csr(graph_data, edge_dir, multigraph)
             graph_idx = from_csr(utils.toindex(indptr), utils.toindex(indices),
                                  multigraph, edge_dir, _get_graph_path(graph_name))
+            self._graph = DGLGraph(graph_idx, multigraph=multigraph, readonly=True)
 
-        self._graph = DGLGraph(graph_idx, multigraph=multigraph, readonly=True)
         self._num_workers = num_workers
         self._graph_name = graph_name
         self._edge_dir = edge_dir
@@ -1046,10 +1055,19 @@ def create_graph_store_server(graph_data, graph_name, store_type, num_workers,
     After the server runs, the graph store clients can access the graph data
     with the specified graph name.
 
+    DGL graph accepts graph data of multiple formats:
+
+    * NetworkX graph,
+    * scipy matrix,
+    * DGLGraph.
+
+    If the input graph data is DGLGraph, the constructed DGLGraph only contains
+    its graph index.
+
     Parameters
     ----------
     graph_data : graph data
-        Data to initialize graph. Same as networkx's semantics.
+        Data to initialize graph.
     graph_name : string
         Define the name of the graph.
     store_type : string

python/dgl/graph.py

@@ -756,10 +756,19 @@ class DGLGraph(DGLBaseGraph):
     Node and edge features are stored as a dictionary from the feature name
     to the feature data (in tensor).
 
+    DGL graph accepts graph data of multiple formats:
+
+    * NetworkX graph,
+    * scipy matrix,
+    * DGLGraph.
+
+    If the input graph data is DGLGraph, the constructed DGLGraph only contains
+    its graph index.
+
     Parameters
     ----------
     graph_data : graph data, optional
-        Data to initialize graph. Same as networkx's semantics.
+        Data to initialize graph.
     node_frame : FrameRef, optional
         Node feature storage.
     edge_frame : FrameRef, optional
@@ -898,7 +907,10 @@ class DGLGraph(DGLBaseGraph):
                  multigraph=None,
                  readonly=False):
         # graph
-        gidx = graph_index.create_graph_index(graph_data, multigraph, readonly)
+        if isinstance(graph_data, DGLGraph):
+            gidx = graph_data._graph
+        else:
+            gidx = graph_index.create_graph_index(graph_data, multigraph, readonly)
         super(DGLGraph, self).__init__(gidx)
 
         # node and edge frame