From f6d2e7a6b66d1da1b5ca75dd87beeec5e5595ecd 2012-03-15 15:34:51
From: Robert Kern <rkern@enthought.com>
Date: 2012-03-15 15:34:51
Subject: [PATCH] BUG: LBYL when clearing the output history on shutdown.

---

diff --git a/IPython/core/displayhook.py b/IPython/core/displayhook.py
index e2e9c0d..5eebb5f 100644
--- a/IPython/core/displayhook.py
+++ b/IPython/core/displayhook.py
@@ -252,7 +252,11 @@ class DisplayHook(Configurable):
             try:
                 del self.shell.user_ns[key]
             except: pass
-        self.shell.user_ns['_oh'].clear()
+        # In some embedded circumstances, the user_ns doesn't have the
+        # '_oh' key set up.
+        oh = self.shell.user_ns.get('_oh', None)
+        if oh is not None:
+            oh.clear()
 
         # Release our own references to objects:
         self._, self.__, self.___ = '', '', ''