Make TraitListObject notify even if list values stay the same

traits/tests/test_trait_list_object.py

@@ -259,9 +259,20 @@ def test_setitem_nochange(self):
 
         tl[3:] = []
         self.assertEqual(tl, [1, 2, 3])
-        self.assertIsNone(self.index)
-        self.assertIsNone(self.removed)
-        self.assertIsNone(self.added)
+        self.assertEqual(self.index, 3)
+        self.assertEqual(self.removed, [])
+        self.assertEqual(self.added, [])
+
+    def test_setitem_nochange_element(self):
+        tl = TraitList([1, 2, 3],
+                       item_validator=int_item_validator,
+                       notifiers=[self.notification_handler])
+
+        tl[0] = 1
+        self.assertEqual(tl, [1, 2, 3])
+        self.assertEqual(self.index, 0)
+        self.assertEqual(self.removed, [1])
+        self.assertEqual(self.added, [1])
 
     def test_setitem_iterable(self):
         tl = TraitList([1, 2, 3],

traits/tests/test_traits.py

@@ -1089,10 +1089,9 @@ def test_trait_list_event(self):
         self.assertLastTraitListEventEqual(0, [6, 7], [4, 5])
         self.obj.alist[0:2:1] = [8, 9]
         self.assertLastTraitListEventEqual(0, [4, 5], [8, 9])
-        old_event = self.last_event
         self.obj.alist[0:2:1] = [8, 9]
-        # If no values changed, no new TraitListEvent will be generated.
-        self.assertIs(self.last_event, old_event)
+        # Even if no values change, a new TraitListEvent will be generated.
+        self.assertLastTraitListEventEqual(0, [8, 9], [8, 9])
         self.obj.alist[0:4:2] = [10, 11]
         self.assertLastTraitListEventEqual(
             slice(0, 4, 2), [8, 4], [10, 11]

traits/trait_list_object.py

@@ -285,8 +285,7 @@ def __setitem__(self, key, value):
                 pass
         super().__setitem__(key, value)
 
-        if added != removed:
-            self.notify(normalized_index, removed, added)
+        self.notify(normalized_index, removed, added)
 
     def append(self, object):
         """ Append object to the end of the list.