Hook the output the right way.

IPython/html/static/widgets/js/widget_output.js

@@ -46,30 +46,14 define([
         /**
          * Handles re-routed iopub messages.
          */
-        _handle_route_msg: function(content) {
-            if (content) {
-                var msg_type = content.type;
-                var json = {
-                    output_type: msg_type
-                };
-
-                var data = content.args[0];
+        _handle_route_msg: function(msg) {
+            if (msg) {
+                var msg_type = msg.msg_type;
                 if (msg_type=='clear_output') {
-                    this.output_area.clear_output(data.wait || false);
-                    return;
-                } else if (msg_type === "stream") {
-                    data = content.kwargs.content;
-                    json.text = data.text;
-                    json.name = data.name;
-                } else if (msg_type === "display_data") {
-                    json.data = data.data;
-                    json.metadata = data.metadata;
+                    this.output_area.handle_clear_output(msg);
                 } else {
-                    console.log("unhandled output message", msg);
-                    return;
+                    this.output_area.handle_output(msg);
                 }
-
-                this.output_area.append_output(json);    
             }
         },
     });

IPython/html/widgets/widget_output.py

@@ -46,12 +46,24 class Output(DOMWidget):
         self._original_send = send
         self._session = session
 
-        def send_hook(stream, msg_or_type, *args, **kwargs):            
-            if stream is kernel.iopub_socket and msg_or_type in ['clear_output', 'stream', 'display_data']:
-                msg = {'type': msg_or_type, 'args': args, 'kwargs': kwargs}
-                self.send(msg)
+        def send_hook(stream, msg_or_type, content=None, parent=None, ident=None,
+             buffers=None, track=False, header=None, metadata=None): 
+
+            # Handle both prebuild messages and unbuilt messages.
+            if isinstance(msg_or_type, dict):
+                msg_type = msg_or_type['msg_type']
+                msg = msg_or_type
             else:
-                send(stream, msg_or_type, *args, **kwargs)
+                msg_type = msg_or_type
+                msg = session.msg(msg_type, content=content, parent=parent, 
+                    header=header, metadata=metadata)
+
+            # If this is a message type that we want to forward, forward it.
+            if stream is kernel.iopub_socket and msg_type in ['clear_output', 'stream', 'display_data']:
+                self.send(msg)
+            else: 
+                send(stream, msg_or_type, content=content, parent=parent, ident=ident,
+                    buffers=buffers, track=track, header=header, metadata=metadata)
 
         session.send = send_hook