Fix deletion bug (set size change while looping)

Author: danielhuici

datalayer/hnsw.py

@@ -356,18 +356,22 @@ def _insert_node_to_layers(self, new_node, enter_point):
             enter_point = currently_found_nn
 
     def _delete_neighbors_connections(self, node):
-         """Given a node, deletes the connections to their neighbors.
-
-         Arguments:
-         node    -- the node to delete
-         """
-
-         logger.debug(f"Deleting neighbors of \"{node.get_id()}\"")
-         for layer in range(node.get_max_layer() + 1):
-             for neighbor in node.get_neighbors_at_layer(layer):
-                 logger.debug(f"Deleting at L{layer} link \"{neighbor.get_id()}\"")
-                 neighbor.remove_neighbor(layer, node)
-                 node.remove_neighbor(layer, neighbor)
+        """Given a node, deletes the connections to their neighbors.
+
+        Arguments:
+        node    -- the node to delete
+        """
+
+        logger.debug(f"Deleting neighbors of \"{node.get_id()}\"")
+        for layer in range(node.get_max_layer() + 1):
+            neighbors_to_remove = set()
+            for neighbor in node.get_neighbors_at_layer(layer):
+                logger.debug(f"Deleting at L{layer} link \"{neighbor.get_id()}\"")
+                neighbors_to_remove.add(neighbor)
+                
+            for neighbor in neighbors_to_remove: # bidirectionally remove links
+                node.remove_neighbor(layer, neighbor)
+                neighbor.remove_neighbor(layer, node)
 
     def _delete_node_dict(self, node):
         """Deletes a node from the dict of the HNSW structure.

tests/unit.py

@@ -60,15 +60,14 @@ def test_search_approximate(self):
         self.assertEqual(actual_founds, expected_founds)
         self.assertEqual(actual_distances, expected_distances)
 
-    @unittest.skip("?")
     def test_deletion(self):
         for hash in HASHES[:5]:
             self.apo_model.delete(HashNode(hash, TLSHHashAlgorithm))
 
         expected_founds = [False, False, False, False, False, True, True, True, True, True]
         actual_founds = []
         for hash in HASHES:
-            found, exact, result_dict = self.apo_model.knn_search(HashNode(hash, TLSHHashAlgorithm), 1)
+            found, _, _ = self.apo_model.knn_search(HashNode(hash, TLSHHashAlgorithm), 1)
             actual_founds.append(found)
 
         self.assertEqual(actual_founds, expected_founds)