[Doc/Feature] Refactor, doc update and behavior fix for graphs (#1983)

* Update graph

* Fix for dgl.graph

* from_scipy

* Replace canonical_etypes with relations

* from_networkx

* Update for hetero_from_relations

* Roll back the change of canonical_etypes to relations

* heterograph

* bipartite

* Update doc

* Fix lint

* Fix lint

* Fix test cases

* Fix

* Fix

* Fix

* Fix

* Fix

* Fix

* Update

* Fix test

* Fix

* Update

* Use DGLError

* Update

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* Fix

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* Update

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* Fix

* Fix

* Update

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* rewrite sanity checks

* delete unnecessary checks

* Update

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* Update

* Fix

* Update

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* Fix

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* Fix

Co-authored-by: xiang song(charlie.song) <classicxsong@gmail.com>
Co-authored-by: Minjie Wang <wmjlyjemaine@gmail.com>
Co-authored-by: Quan Gan <coin2028@hotmail.com>

python/dgl/nn/mxnet/conv/gatedgraphconv.py

@@ -76,8 +76,9 @@ class GatedGraphConv(nn.Block):
             is the output feature size.
         """
         with graph.local_scope():
-            assert graph.is_homogeneous(), \
-                "not a homograph; convert it with to_homo and pass in the edge type as argument"
+            assert graph.is_homogeneous, \
+                "not a homogeneous graph; convert it with to_homogeneous " \
+                "and pass in the edge type as argument"
             zero_pad = nd.zeros((feat.shape[0], self._out_feats - feat.shape[1]),
                                 ctx=feat.context)
             feat = nd.concat(feat, zero_pad, dim=-1)

python/dgl/nn/mxnet/conv/relgraphconv.py

@@ -229,8 +229,9 @@ class RelGraphConv(gluon.Block):
         mx.ndarray.NDArray
             New node features.
         """
-        assert g.is_homogeneous(), \
-            "not a homograph; convert it with to_homo and pass in the edge type as argument"
+        assert g.is_homogeneous, \
+            "not a homogeneous graph; convert it with to_homogeneous " \
+            "and pass in the edge type as argument"
         with g.local_scope():
             g.ndata['h'] = x
             g.edata['type'] = etypes

python/dgl/nn/mxnet/conv/tagconv.py

@@ -106,7 +106,7 @@ class TAGConv(gluon.Block):
             is size of output feature.
         """
         with graph.local_scope():
-            assert graph.is_homogeneous(), 'Graph is not homogeneous'
+            assert graph.is_homogeneous, 'Graph is not homogeneous'
 
             degs = graph.in_degrees().astype('float32')
             norm = mx.nd.power(mx.nd.clip(degs, a_min=1, a_max=float("inf")), -0.5)