Merge pull request jupyter-widgets#3484 from xiaochen-db/check-keys-for-echo-update

Check self.keys before accessing trait in set_state()

Author: jasongrout

python/ipywidgets/ipywidgets/widgets/tests/test_set_state.py

@@ -304,8 +304,8 @@ class ValueWidget(Widget):
     assert widget.value == 1
 
     widget._send = mock.MagicMock()
-    # this mimics a value coming from the front end
-    widget.set_state({'value': 42})
+    # this mimics a state coming from the front end
+    widget.set_state({'value': 42, 'unexpected_field': 43})
     assert widget.value == 42
 
     # we expect this to be echoed

python/ipywidgets/ipywidgets/widgets/widget.py

@@ -566,8 +566,8 @@ def set_state(self, sync_data):
         # Send an echo update message immediately
         if JUPYTER_WIDGETS_ECHO:
             echo_state = {}
-            for attr,value in sync_data.items():
-                if self.trait_metadata(attr, 'echo_update', default=True):
+            for attr, value in sync_data.items():
+                if attr in self.keys and self.trait_metadata(attr, 'echo_update', default=True):
                     echo_state[attr] = value
             if echo_state:
                 echo_state, echo_buffer_paths, echo_buffers = _remove_buffers(echo_state)