Merge pull request #1691 from minrk/1442

Closes  #1442: bug in messaging when cache size is set to 0.

IPython/frontend/qt/console/ipython_widget.py

@@ -214,7 +214,7 b' class IPythonWidget(FrontendWidget):'
         self.log.debug("pyout: %s", msg.get('content', ''))
         if not self._hidden and self._is_from_this_session(msg):
             content = msg['content']
-            prompt_number = content['execution_count']
+            prompt_number = content.get('execution_count', 0)
             data = content['data']
             if data.has_key('text/html'):
                 self._append_plain_text(self.output_sep, True)

IPython/frontend/qt/console/rich_ipython_widget.py

@@ -96,7 +96,7 b' class RichIPythonWidget(IPythonWidget):'
         """
         if not self._hidden and self._is_from_this_session(msg):
             content = msg['content']
-            prompt_number = content['execution_count']
+            prompt_number = content.get('execution_count', 0)
             data = content['data']
             if data.has_key('image/svg+xml'):
                 self._pre_image_append(msg, prompt_number)

IPython/zmq/displayhook.py

@@ -57,8 +57,7 b' class ZMQShellDisplayHook(DisplayHook):'
 
     def write_output_prompt(self):
         """Write the output prompt."""
-        if self.do_full_cache:
-            self.msg['content']['execution_count'] = self.prompt_count
+        self.msg['content']['execution_count'] = self.prompt_count
 
     def write_format_data(self, format_dict):
         _encode_binary(format_dict)