Don't log complete contents of history replies, even in debug

IPython/frontend/qt/console/ipython_widget.py

@@ -179,7 +179,6 b' class IPythonWidget(FrontendWidget):'
         """ Implemented to handle history tail replies, which are only supported
             by the IPython kernel.
         """
-        self.log.debug("history: %s", msg.get('content', ''))
         content = msg['content']
         if 'history' not in content:
             self.log.error("History request failed: %r"%content)
@@ -199,6 +198,7 b' class IPythonWidget(FrontendWidget):'
         # reset retry flag
         self._retrying_history_request = False
         history_items = content['history']
+        self.log.debug("Received history reply with %i entries", len(history_items))
         items = []
         last_cell = u""
         for _, _, cell in history_items:

IPython/zmq/ipkernel.py

@@ -391,11 +391,12 b' class Kernel(Configurable):'
 
         else:
             hist = []
-        content = {'history' : list(hist)}
+        hist = list(hist)
+        content = {'history' : hist}
         content = json_clean(content)
         msg = self.session.send(self.shell_socket, 'history_reply',
                                 content, parent, ident)
-        self.log.debug(str(msg))
+        self.log.debug("Sending history reply with %i entries", len(hist))
 
     def connect_request(self, ident, parent):
         if self._recorded_ports is not None: