Merge pull request #5197 from jasongrout/traitlet-notify

If there is an error comparing traitlet values when setting a trait, default to go ahead and notify of the new value.

IPython/utils/traitlets.py

@@ -371,7 +371,12 b' class TraitType(object):'
         new_value = self._validate(obj, value)
         old_value = self.__get__(obj)
         obj._trait_values[self.name] = new_value
-        if old_value != new_value:
+        try:
+            notify = (old_value != new_value)
+        except:
+            # if there is an error in comparing, default to notify
+            notify = True
+        if notify:
             obj._notify_trait(self.name, old_value, new_value)
 
     def _validate(self, obj, value):