From edfa4edabc3f9493871def07c183a4914a5b0b2d 2014-11-12 19:29:10
From: Min RK <benjaminrk@gmail.com>
Date: 2014-11-12 19:29:10
Subject: [PATCH] handle setting Widget.comm = None

which is done in `Widget.close`

fixes loads of warnings in widget test output, caused every time a widget is closed.
---

diff --git a/IPython/html/widgets/widget.py b/IPython/html/widgets/widget.py
index 0eccf42..5a398fc 100644
--- a/IPython/html/widgets/widget.py
+++ b/IPython/html/widgets/widget.py
@@ -175,7 +175,8 @@ class Widget(LoggingConfigurable):
 
     def _comm_changed(self, name, new):
         """Called when the comm is changed."""
-        self.comm = new
+        if new is None:
+            return
         self._model_id = self.model_id
         
         self.comm.on_msg(self._handle_msg)