Update predecessors/successors in edge subgraphdigraph-edge-subgraph

2 files changed, 20 insertions, 5 deletions

diff --git a/networkx/classes/digraph.py b/networkx/classes/digraph.py
index 9e086536..df8f7260 100644
--- a/networkx/classes/digraph.py
+++ b/networkx/classes/digraph.py
@@ -1324,16 +1324,17 @@ class DiGraph(Graph):
         for u, v in edges:
             # Copy the node attributes if they haven't been copied
             # already.
+            #
+            # Also, create an entry in the successors and predecessors
+            # dictionary for the nodes u and v.
             if u not in H.node:
                 H.node[u] = self.node[u]
+                H.pred[u] = H.adjlist_inner_dict_factory()
+                H.succ[u] = H.adjlist_inner_dict_factory()
             if v not in H.node:
                 H.node[v] = self.node[v]
-            # Create an entry in the successors and predecessors
-            # dictionary for the nodes u and v if they don't exist yet.
-            if u not in H.succ:
-                H.succ[u] = H.adjlist_inner_dict_factory()
-            if v not in H.pred:
                 H.pred[v] = H.adjlist_inner_dict_factory()
+                H.succ[v] = H.adjlist_inner_dict_factory()
             # Copy the edge attributes.
             H.edge[u][v] = self.edge[u][v]
             H.pred[v][u] = self.pred[v][u]
diff --git a/networkx/classes/tests/test_digraph.py b/networkx/classes/tests/test_digraph.py
index 64f8855a..eee86e37 100644
--- a/networkx/classes/tests/test_digraph.py
+++ b/networkx/classes/tests/test_digraph.py
@@ -260,3 +260,17 @@ class TestEdgeSubgraph(TestGraphEdgeSubgraph):
         # Get the subgraph induced by the first and last edges.
         self.G = G
         self.H = G.edge_subgraph([(0, 1), (3, 4)])
+
+    def test_pred_succ(self):
+        """Test that nodes are added to predecessors and successors.
+
+        For more information, see GitHub issue #2370.
+
+        """
+        G = networkx.DiGraph()
+        G.add_edge(0, 1)
+        H = G.edge_subgraph([(0, 1)])
+        assert_equal(list(H.predecessors(0)), [])
+        assert_equal(list(H.successors(0)), [1])
+        assert_equal(list(H.predecessors(1)), [0])
+        assert_equal(list(H.successors(1)), [])