Merge pull request jupyter-widgets#1523 from jasongrout/json

Comparing the json representation should handle idiosyncracies of python->json datastructures

ipywidgets/widgets/widget.py

@@ -17,6 +17,7 @@
     Undefined)
 from ipython_genutils.py3compat import string_types, PY3
 from IPython.display import display
+from json import loads as jsonloads, dumps as jsondumps
 
 from base64 import standard_b64decode, standard_b64encode
 
@@ -595,8 +596,11 @@ def hold_sync(self):
     def _should_send_property(self, key, value):
         """Check the property lock (property_lock)"""
         to_json = self.trait_metadata(key, 'to_json', self._trait_to_json)
+        # A roundtrip conversion through json in the comparison takes care of
+        # idiosyncracies of how python data structures map to json, for example
+        # tuples get converted to lists.
         if (key in self._property_lock
-            and to_json(value, self) == self._property_lock[key]):
+            and jsonloads(jsondumps(to_json(value, self))) == self._property_lock[key]):
             return False
         elif self._holding_sync:
             self._states_to_send.add(key)