[HeteroGraph] Improve Error Messages for find_edges (#1626)

* Improve error message

* Fix

* Fix
Co-authored-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>

python/dgl/heterograph.py

@@ -1514,6 +1514,18 @@ class DGLHeteroGraph(object):
         (tensor([0, 1]), tensor([0, 2]))
         """
         check_same_dtype(self._idtype_str, eid)
+        if F.is_tensor(eid):
+            max_eid = F.max(eid, dim=0)
+        else:
+            max_eid = np.max(eid, axis=0)
+        max_valid_eid = self.number_of_edges(etype) - 1
+        valid_ids = max_eid <= max_valid_eid
+        if etype is None:
+            assert valid_ids, \
+                'Expect edge ids to be in [0, ..., {:d}], got {}'.format(max_valid_eid, max_eid)
+        else:
+            assert valid_ids, 'Expect edge ids to be in [0, ..., {:d}]' \
+                              ' for type {}, got {}'.format(max_valid_eid, etype, max_eid)
         eid = utils.toindex(eid, self._idtype_str)
         src, dst, _ = self._graph.find_edges(self.get_etype_id(etype), eid)
         return src.tousertensor(), dst.tousertensor()

tests/compute/test_heterograph.py

@@ -238,7 +238,8 @@ def test_query(index_dtype):
             assert F.asnumpy(e).tolist() == list(range(n_edges))
 
             # find_edges
-            u, v = g.find_edges(list(range(n_edges)), etype)
+            for edge_ids in [list(range(n_edges)), np.arange(n_edges), F.astype(F.arange(0, n_edges), g.idtype)]:
+                u, v = g.find_edges(edge_ids, etype)
                 assert F.asnumpy(u).tolist() == srcs
                 assert F.asnumpy(v).tolist() == dsts