Remove __len__ method from DGLGraph (dmlc#2902)

* Update heterograph.py

* remove unit tests

* replace tutorial

python/dgl/heterograph.py

@@ -2447,13 +2447,6 @@ def num_edges(self, etype=None):
         else:
             return self._graph.number_of_edges(self.get_etype_id(etype))
 
-    def __len__(self):
-        """Deprecated: please directly call :func:`number_of_nodes`
-        """
-        dgl_warning('DGLGraph.__len__ is deprecated.'
-                    'Please directly call DGLGraph.number_of_nodes.')
-        return self.number_of_nodes()
-
     @property
     def is_multigraph(self):
         """Return whether the graph is a multigraph with parallel edges.

tests/compute/test_graph.py

@@ -59,7 +59,6 @@ def test_query():
     def _test_one(g):
         assert g.number_of_nodes() == 10
         assert g.number_of_edges() == 20
-        assert len(g) == 10
 
         for i in range(10):
             assert g.has_node(i)
@@ -131,7 +130,6 @@ def _test(g):
     def _test_csr_one(g):
         assert g.number_of_nodes() == 10
         assert g.number_of_edges() == 20
-        assert len(g) == 10
 
         for i in range(10):
             assert g.has_node(i)

tutorials/models/1_gnn/4_rgcn.py

@@ -313,7 +313,7 @@ def forward(self, g):
 g.edata.update({'rel_type': edge_type, 'norm': edge_norm})
 
 # create model
-model = Model(len(g),
+model = Model(g.num_nodes(),
               n_hidden,
               num_classes,
               num_rels,