del Widget.widgets[seld.model_id] in close rather than in __del__

IPython/html/widgets/widget.py

@@ -127,8 +127,6 b' class Widget(LoggingConfigurable):'
     def __del__(self):
         """Object disposal"""
         self.close()
-        del Widget.widgets[self.model_id]
-        self._comm = None
 
     #-------------------------------------------------------------------------
     # Properties
@@ -166,6 +164,7 b' class Widget(LoggingConfigurable):'
         Closes the underlying comm.
         When the comm is closed, all of the widget views are automatically
         removed from the front-end."""
+        del Widget.widgets[self.model_id]
         if self._comm is not None:
             self._comm.close()