Make Python push initial state.

Also added initial state push callback.

IPython/html/static/widgets/js/manager.js

@@ -190,7 +190,7 define([
         return this.create_model({model_name: msg.content.data.target_name, comm: comm});
     };
 
-    WidgetManager.prototype.create_model = function (model_name, target_name) {
+    WidgetManager.prototype.create_model = function (model_name, target_name, init_state_callback) {
         // Create and return a new widget model.
         //
         // Parameters
@@ -199,7 +199,13 define([
         //      Target name of the widget model to create.
         // target_name: string
         //      Target name of the widget in the back-end.
-        return this._create_model({model_name: model_name, target_name: target_name});
+        // init_state_callback: (optional) callback
+        //      Called when the first state push from the back-end is 
+        //      recieved.
+        return this._create_model({
+            model_name: model_name, 
+            target_name: target_name,
+            init_state_callback: init_state_callback});
     };
 
     WidgetManager.prototype._create_model = function (options) {
@@ -214,6 +220,9 define([
         //      target_name: (optional) string
         //          Target name of the widget in the back-end.
         //      comm: (optional) Comm
+        //      init_state_callback: (optional) callback
+        //          Called when the first state push from the back-end is 
+        //          recieved.
 
         // Create a comm if it wasn't provided.
         var comm = options.comm;
@@ -226,8 +235,8 define([
         
         var instantiate_model = function(ModelType) {
             var model_id = comm.comm_id;
-            var widget_model = new ModelType(that, model_id, comm);
-            widget_model.on('comm:close', function () {sss
+            var widget_model = new ModelType(that, model_id, comm, options.init_state_callback);
+            widget_model.on('comm:close', function () {
               delete that._models[model_id];
             });
             that._models[model_id] = widget_model;

IPython/html/static/widgets/js/widget.js

@@ -9,7 +9,7 define(["widgets/js/manager",
 ], function(widgetmanager, _, Backbone, $, IPython){
 
     var WidgetModel = Backbone.Model.extend({
-        constructor: function (widget_manager, model_id, comm) {
+        constructor: function (widget_manager, model_id, comm, init_state_callback) {
             // Constructor
             //
             // Creates a WidgetModel instance.
@@ -20,7 +20,11 define(["widgets/js/manager",
             // model_id : string
             //      An ID unique to this model.
             // comm : Comm instance (optional)
+            // init_state_callback : callback (optional)
+            //      Called once when the first state message is recieved from 
+            //      the back-end.
             this.widget_manager = widget_manager;
+            this.init_state_callback = init_state_callback;
             this._buffered_state_diff = {};
             this.pending_msgs = 0;
             this.msg_buffer = null;
@@ -70,6 +74,10 define(["widgets/js/manager",
             switch (method) {
                 case 'update':
                     this.set_state(msg.content.data.state);
+                    if (this.init_state_callback) {
+                        this.init_state_callback.apply(this, [this]);
+                        this.init_state_callback = null;
+                    }
                     break;
                 case 'custom':
                     this.trigger('msg:custom', msg.content.data.content);

IPython/html/widgets/widget.py

@@ -142,7 +142,7 class Widget(LoggingConfigurable):
 
         Widget._call_widget_constructed(self)
         if open_comm:
-            self.open()
+        self.open()
 
     def __del__(self):
         """Object disposal"""
@@ -161,17 +161,18 class Widget(LoggingConfigurable):
             if self._model_id is not None:
                 args['comm_id'] = self._model_id
             self.set_comm(Comm(**args))
-            
-            # first update
-            self.send_state()
 
     def set_comm(self, comm):
         """Set's the comm of the widget."""
         self.comm = comm
-        self._model_id = self.model_id
+            self._model_id = self.model_id
+            
+            self.comm.on_msg(self._handle_msg)
+            Widget.widgets[self.model_id] = self
             
-        self.comm.on_msg(self._handle_msg)
-        Widget.widgets[self.model_id] = self
+        # first update
+        self.send_state()
+
 
     @property
     def model_id(self):