[Hetero] Improve speed of several Hetero APIs (#1486)

* add clone function to frame

* add utest

* replace all local_var with local_scope

* fix utest

* avoid creating canonical types in __getitem__

* lint

* try another utest  appraoch for mx

* utest

python/dgl/random.py

@@ -70,7 +70,7 @@ def choice(a, size, replace=True, prob=None):  # pylint: disable=invalid-name
         population = a
 
     if prob is None:
-        prob = nd.null()
+        prob = nd.NULL
     else:
         prob = F.zerocopy_to_dgl_ndarray(prob)
 

python/dgl/transform.py

@@ -894,7 +894,7 @@ def to_block(g, dst_nodes=None, include_dst_in_src=True):
         if nodes is not None:
             dst_nodes_nd.append(F.zerocopy_to_dgl_ndarray(nodes))
         else:
-            dst_nodes_nd.append(nd.null())
+            dst_nodes_nd.append(nd.NULL)
 
     new_graph_index, src_nodes_nd, induced_edges_nd = _CAPI_DGLToBlock(
         g._graph, dst_nodes_nd, include_dst_in_src)
@@ -945,7 +945,7 @@ def remove_edges(g, edge_ids):
                 "Graph has more than one edge type; specify a dict for edge_id instead.")
         edge_ids = {g.canonical_etypes[0]: edge_ids}
 
-    edge_ids_nd = [nd.null()] * len(g.etypes)
+    edge_ids_nd = [nd.NULL] * len(g.etypes)
     for key, value in edge_ids.items():
         edge_ids_nd[g.get_etype_id(key)] = F.zerocopy_to_dgl_ndarray(value)
     new_graph_index, induced_eids_nd = _CAPI_DGLRemoveEdges(g._graph, edge_ids_nd)

tests/compute/test_frame.py

@@ -360,6 +360,23 @@ def test_inplace():
     newa2addr = id(f['a2'])
     assert a2addr == newa2addr
 
+@unittest.skipIf(dgl.backend.backend_name == "tensorflow", reason="TF doesn't support inplace update")
+def test_clone():
+    f = FrameRef(Frame(create_test_data()))
+    f1 = f.clone()
+    f2 = f.deepclone()
+
+    f1['b'] = F.randn((N, D))
+    f2['c'] = F.randn((N, D))
+    assert 'b' not in f
+    assert 'c' not in f
+
+    f1['a1'][0, 0] = -10.
+    assert float(F.asnumpy(f['a1'][0, 0])) == -10.
+    x = float(F.asnumpy(f['a2'][0, 0]))
+    f2['a2'][0, 0] = -10.
+    assert float(F.asnumpy(f['a2'][0, 0])) == x
+
 def _reconstruct_pickle(obj):
     f = io.BytesIO()
     pickle.dump(obj, f)