Merge pull request #8124 from jdfreder/dynamic

Dynamic traits.

IPython/html/widgets/widget.py

@@ -292,6 +292,13 @@ class Widget(LoggingConfigurable):
             True if the callback should be unregistered."""
         self._display_callbacks.register_callback(callback, remove=remove)
 
+    def add_trait(self, traitname, trait):
+        """Dynamically add a trait attribute to the Widget."""
+        super(Widget, self).add_trait(traitname, trait)
+        if trait.get_metadata('sync'):
+             self.keys.append(traitname)
+             self.send_state(traitname)
+
     #-------------------------------------------------------------------------
     # Support methods
     #-------------------------------------------------------------------------