fix date objects in _reserialize_reply

IPython/frontend/html/notebook/handlers.py

@@ -30,6 +30,7 b' from zmq.utils import jsonapi'
 from IPython.external.decorator import decorator
 from IPython.zmq.session import Session
 from IPython.lib.security import passwd_check
+from IPython.utils.jsonutil import date_default
 
 try:
     from docutils.core import publish_string
@@ -385,13 +386,13 b' class ZMQStreamHandler(websocket.WebSocketHandler):'
         except KeyError:
             pass
         msg.pop('buffers')
-        return jsonapi.dumps(msg)
+        return jsonapi.dumps(msg, default=date_default)
 
     def _on_zmq_reply(self, msg_list):
         try:
             msg = self._reserialize_reply(msg_list)
-        except:
-            self.application.log.critical("Malformed message: %r" % msg_list)
+        except Exception:
+            self.application.log.critical("Malformed message: %r" % msg_list, exc_info=True)
         else:
             self.write_message(msg)