Re-decoupled comm_id from widget models

IPython/html/static/notebook/js/widgetmanager.js

@@ -1,208 +1,210 b''
 //----------------------------------------------------------------------------
 //  Copyright (C) 2013  The IPython Development Team
 //
 //  Distributed under the terms of the BSD License.  The full license is in
 //  the file COPYING, distributed as part of this software.
 //----------------------------------------------------------------------------
 
 //============================================================================
 // WidgetModel, WidgetView, and WidgetManager
 //============================================================================
 /**
  * Base Widget classes
  * @module IPython
  * @namespace IPython
  * @submodule widget
  */
 
 (function () {
     "use strict";
 
     // Use require.js 'define' method so that require.js is intelligent enough to
     // syncronously load everything within this file when it is being 'required' 
     // elsewhere.
     define(["underscore",
              "backbone",
             ], function (underscore, backbone) {
 
         //--------------------------------------------------------------------
         // WidgetManager class
         //--------------------------------------------------------------------
         var WidgetManager = function () {
             this.comm_manager = null;
             this.widget_model_types = {};
             this.widget_view_types = {};
             this._model_instances = {};
             
             Backbone.sync = function (method, model, options, error) {
                 var result = model._handle_sync(method, options);
                 if (options.success) {
                   options.success(result);
                 }
             }; 
         };
 
 
         WidgetManager.prototype.attach_comm_manager = function (comm_manager) {
             this.comm_manager = comm_manager;
 
             // Register already-registered widget model types with the comm manager.
             for (var widget_model_name in this.widget_model_types) {
                 this.comm_manager.register_target(widget_model_name, $.proxy(this._handle_comm_open, this));
             }
         };
 
 
         WidgetManager.prototype.register_widget_model = function (widget_model_name, widget_model_type) {
             // Register the widget with the comm manager.  Make sure to pass this object's context
             // in so `this` works in the call back.
             if (this.comm_manager !== null) {
                 this.comm_manager.register_target(widget_model_name, $.proxy(this._handle_comm_open, this));
             }
             this.widget_model_types[widget_model_name] = widget_model_type;
         };
 
 
         WidgetManager.prototype.register_widget_view = function (widget_view_name, widget_view_type) {
             this.widget_view_types[widget_view_name] = widget_view_type;
         };
+
+
     WidgetManager.prototype.handle_msg = function(msg, model) {
         var method = msg.content.data.method;
         switch (method) {
         case 'display':
             var cell = this.get_msg_cell(msg.parent_header.msg_id);
             if (cell === null) {
             console.log("Could not determine where the display" + 
                     " message was from.  Widget will not be displayed");
             } else {
             var view = this.create_view(model, 
                             msg.content.data.view_name, cell);
             if (view !== undefined 
                 && cell.widget_subarea !== undefined 
                 && cell.widget_subarea !== null) {
                             cell.widget_area.show();
                             cell.widget_subarea.append(view.$el);
             }
             }
             break;
         }
     }
 
     WidgetManager.prototype.create_view = function(model, view_name, cell) {
         view_name = view_name || model.get('default_view_name');
             var ViewType = this.widget_view_types[view_name];
             if (ViewType !== undefined && ViewType !== null) {
                 var view = new ViewType({model: model, widget_manager: this, cell: cell});
                 view.render();
         model.views.push(view);
         model.on('destroy', view.remove, view);
         /*
                 // TODO: handle view deletion.  Don't forget to delete child views
                 var that = this;
                 view.$el.on("remove", function () { 
                     var index = that.views.indexOf(view);
                     if (index > -1) {
                         that.views.splice(index, 1);
                     }
                     view.remove(); // Clean-up view 
 
                     // Close the comm if there are no views left.
                     if (that.views.length() === 0) {
             //trigger comm close event?
                         }
 
                 
                         if (that.comm !== undefined) {
                             that.comm.close();
                             delete that.comm.model; // Delete ref so GC will collect widget model.
                             delete that.comm;
                         }
-                        delete that.widget_id; // Delete id from model so widget manager cleans up.
+                            delete that.model_id; // Delete id from model so widget manager cleans up.
                     });
         */
                 return view;
             }
         },
 
         WidgetManager.prototype.get_msg_cell = function (msg_id) {
         var cell = null;
             // First, check to see if the msg was triggered by cell execution.
             if (IPython.notebook !== undefined && IPython.notebook !== null) {
                 cell = IPython.notebook.get_msg_cell(msg_id);
             }
         if (cell !== null) {
         return cell
         }
             // Second, check to see if a get_cell callback was defined
             // for the message.  get_cell callbacks are registered for
             // widget messages, so this block is actually checking to see if the
             // message was triggered by a widget.
             var kernel = this.get_kernel();
             if (kernel !== undefined && kernel !== null) {
                 var callbacks = kernel.get_callbacks_for_msg(msg_id);
                 if (callbacks !== undefined && 
                     callbacks.iopub !== undefined && 
                     callbacks.iopub.get_cell !== undefined) {
 
                     return callbacks.iopub.get_cell();
                 }    
             }
             
             // Not triggered by a cell or widget (no get_cell callback 
             // exists).
             return null;
         };
 
 
-        WidgetManager.prototype.get_model = function (widget_id) {
-            var model = this._model_instances[widget_id];
-            if (model !== undefined && model.id == widget_id) {
+        WidgetManager.prototype.get_model = function (model_id) {
+            var model = this._model_instances[model_id];
+            if (model !== undefined && model.id == model_id) {
                 return model;
             }
             return null;
         };
 
 
         WidgetManager.prototype.get_kernel = function () {
             if (this.comm_manager === null) {
                 return null;
             } else {
                 return this.comm_manager.kernel;
             }
         };
 
 
         WidgetManager.prototype.on_create_widget = function (callback) {
             this._create_widget_callback = callback;
         };
 
 
         WidgetManager.prototype._handle_create_widget = function (widget_model) {
             if (this._create_widget_callback) {
                 try {
                     this._create_widget_callback(widget_model);
                 } catch (e) {
                     console.log("Exception in WidgetManager callback", e, widget_model);
                 }
             }
         };
 
 
         WidgetManager.prototype._handle_comm_open = function (comm, msg) {
             var widget_type_name = msg.content.target_name;
             var widget_model = new this.widget_model_types[widget_type_name](this, comm.comm_id, comm);
-            this._model_instances[comm.comm_id] = widget_model;
+            this._model_instances[comm.comm_id] = widget_model; // comm_id == model_id
             this._handle_create_widget(widget_model);
         };
         
         //--------------------------------------------------------------------
         // Init code
         //--------------------------------------------------------------------
         IPython.WidgetManager = WidgetManager;
         if (IPython.widget_manager === undefined || IPython.widget_manager === null) {
             IPython.widget_manager = new WidgetManager();    
         }
 
         return IPython.widget_manager;
     });
 }());

IPython/html/static/notebook/js/widgets/base.js

@@ -1,345 +1,345 b''
 //----------------------------------------------------------------------------
 //  Copyright (C) 2013 The IPython Development Team
 //
 //  Distributed under the terms of the BSD License.  The full license is in
 //  the file COPYING, distributed as part of this software.
 //----------------------------------------------------------------------------
 
 //============================================================================
 // Base Widget Model and View classes
 //============================================================================
 
 /**
  * @module IPython
  * @namespace IPython
  **/
 
 define(["notebook/js/widgetmanager",
         "underscore",
         "backbone"], 
 function(widget_manager, underscore, backbone){
     
     //--------------------------------------------------------------------
     // WidgetModel class
     //--------------------------------------------------------------------
     var WidgetModel = Backbone.Model.extend({
-        constructor: function (widget_manager, widget_id, comm) {
+        constructor: function (widget_manager, model_id, comm) {
             this.widget_manager = widget_manager;
             this.pending_msgs = 0;
             this.msg_throttle = 3;
             this.msg_buffer = null;
-            this.id = widget_id;
+            this.id = model_id;
             this.views = [];
 
             if (comm !== undefined) {
                 // Remember comm associated with the model.
                 this.comm = comm;
                 comm.model = this;
 
                 // Hook comm messages up to model.
                 comm.on_close($.proxy(this._handle_comm_closed, this));
                 comm.on_msg($.proxy(this._handle_comm_msg, this));
             }
             return Backbone.Model.apply(this);
         },
 
         send: function (content, callbacks) {
             if (this.comm !== undefined) {
                 var data = {method: 'custom', custom_content: content};
                 this.comm.send(data, callbacks);
             }
         },
 
         // Handle when a widget is closed.
         _handle_comm_closed: function (msg) {
             this.trigger('comm:close');
             delete this.comm.model; // Delete ref so GC will collect widget model.
             delete this.comm;
-            delete this.widget_id; // Delete id from model so widget manager cleans up.
+            delete this.model_id; // Delete id from model so widget manager cleans up.
             // TODO: Handle deletion, like this.destroy(), and delete views, etc.
         },
 
 
         // Handle incoming comm msg.
         _handle_comm_msg: function (msg) {
             var method = msg.content.data.method;
             switch (method) {
                 case 'update':
                     this.apply_update(msg.content.data.state);
                     break;
                 case 'custom':
                     this.trigger('msg:custom', msg.content.data.custom_content);
                     break;
                 default:
                     // pass on to widget manager
                     this.widget_manager.handle_msg(msg, this);
             }
         },
 
 
         // Handle when a widget is updated via the python side.
         apply_update: function (state) {
             this.updating = true;
             try {
                 for (var key in state) {
                     if (state.hasOwnProperty(key)) {
                             this.set(key, state[key]);
                     }
                 }
                 //TODO: are there callbacks that make sense in this case?  If so, attach them here as an option
                 this.save();
             } finally {
                 this.updating = false;
             }
         },
 
 
         _handle_status: function (msg, callbacks) {
             //execution_state : ('busy', 'idle', 'starting')
             if (this.comm !== undefined && msg.content.execution_state ==='idle') {
                 // Send buffer if this message caused another message to be
                 // throttled.
                 if (this.msg_buffer !== null &&
                     this.msg_throttle === this.pending_msgs) {
                     var data = {method: 'backbone', sync_method: 'update', sync_data: this.msg_buffer};
                     this.comm.send(data, callbacks);   
                     this.msg_buffer = null;
                 } else {
                     // Only decrease the pending message count if the buffer
                     // doesn't get flushed (sent).
                     --this.pending_msgs;
                 }
             }
         },
 
 
         // Custom syncronization logic.
         _handle_sync: function (method, options) {
             var model_json = this.toJSON();
             var attr;
 
             // Only send updated state if the state hasn't been changed 
             // during an update.
             if (this.comm !== undefined) {
                 if (!this.updating) {
                     if (this.pending_msgs >= this.msg_throttle) {
                         // The throttle has been exceeded, buffer the current msg so
                         // it can be sent once the kernel has finished processing 
                         // some of the existing messages.
                         if (method=='patch') {
                             if (this.msg_buffer === null) {
                                 this.msg_buffer = $.extend({}, model_json); // Copy
                             }
                             for (attr in options.attrs) {
                                 this.msg_buffer[attr] = options.attrs[attr];
                             }
                         } else {
                             this.msg_buffer = $.extend({}, model_json); // Copy
                         }
 
                     } else {
                         // We haven't exceeded the throttle, send the message like 
                         // normal.  If this is a patch operation, just send the 
                         // changes.
                         var send_json = model_json;
                         if (method =='patch') {
                             send_json = {};
                             for (attr in options.attrs) {
                                 send_json[attr] = options.attrs[attr];
                             }
                         }
 
                         var data = {method: 'backbone', sync_method: method, sync_data: send_json};
                         this.comm.send(data, options.callbacks);
                         this.pending_msgs++;
                     }
                 }
             }
             
             // Since the comm is a one-way communication, assume the message 
             // arrived.
             return model_json;
         },
 
     });
 
 
     //--------------------------------------------------------------------
     // WidgetView class
     //--------------------------------------------------------------------
     var BaseWidgetView = Backbone.View.extend({
         initialize: function(options) {
             this.model.on('change',this.update,this);
             this.widget_manager = options.widget_manager;
             this.comm_manager = options.widget_manager.comm_manager;
             this.cell = options.cell;
             this.child_views = [];
         },
 
         update: function(){
             // update view to be consistent with this.model
             // triggered on model change
         },
 
-        child_view: function(comm_id, view_name) {
+        child_view: function(model_id, view_name) {
             // create and return a child view, given a comm id for a model and (optionally) a view name
             // if the view name is not given, it defaults to the model's default view attribute
-            var child_model = this.comm_manager.comms[comm_id].model;
+            var child_model = this.widget_manager.get_model(model_id);
             var child_view = this.widget_manager.create_view(child_model, view_name, this.cell);
-            this.child_views[comm_id] = child_view;
+            this.child_views[model_id] = child_view;
             return child_view;
         },
         
         update_child_views: function(old_list, new_list) {
             // this function takes an old list and new list of comm ids
             // views in child_views that correspond to deleted ids are deleted
             // views corresponding to added ids are added child_views
         
             // delete old views
             _.each(_.difference(old_list, new_list), function(element, index, list) {
                 var view = this.child_views[element];
                 delete this.child_views[element];
                 view.remove();
             }, this);
             
             // add new views
             _.each(_.difference(new_list, old_list), function(element, index, list) {
                 // this function adds the view to the child_views dictionary
                 this.child_view(element);
             }, this);
         },
 
         
 
         render: function(){
             // render the view.  By default, this is only called the first time the view is created
         },
         send: function (content) {
             this.model.send(content, this._callbacks());
         },
 
         touch: function () {
             this.model.save(this.model.changedAttributes(), {patch: true, callbacks: this._callbacks()});
         },
 
         _callbacks: function () {
             // callback handlers specific to this view's cell
             var callbacks = {};
             var cell = this.cell;
             if (cell !== null) {
                 // Try to get output handlers
                 var handle_output = null;
                 var handle_clear_output = null;
                 if (cell.output_area !== undefined && cell.output_area !== null) {
                     handle_output = $.proxy(cell.output_area.handle_output, cell.output_area);
                     handle_clear_output = $.proxy(cell.output_area.handle_clear_output, cell.output_area);
                 }
 
                 // Create callback dict using what is known
                 var that = this;
                 callbacks = {
                     iopub : {
                         output : handle_output,
                         clear_output : handle_clear_output,
 
                         status : function (msg) {
                             that.model._handle_status(msg, that._callbacks());
                         },
 
                         // Special function only registered by widget messages.
                         // Allows us to get the cell for a message so we know
                         // where to add widgets if the code requires it.
                         get_cell : function () {
                             return cell;
                         },
                     },
                 };
             }
             return callbacks;
         },
 
     });
 
     var WidgetView = BaseWidgetView.extend({
         initialize: function (options) {
             // TODO: make changes more granular (e.g., trigger on visible:change)
             this.model.on('change', this.update, this);
             this.model.on('msg:custom', this.on_msg, this);
             BaseWidgetView.prototype.initialize.apply(this, arguments);
         },
         
         on_msg: function(msg) {
             switch(msg.msg_type) {
                 case 'add_class':
                     this.add_class(msg.selector, msg.class_list);
                     break;
                 case 'remove_class':
                     this.remove_class(msg.selector, msg.class_list);
                     break;
             }
         },
 
         add_class: function (selector, class_list) {
             var elements = this._get_selector_element(selector);
             if (elements.length > 0) {
                 elements.addClass(class_list);
             }
         },
         
         remove_class: function (selector, class_list) {
             var elements = this._get_selector_element(selector);
             if (elements.length > 0) {
                 elements.removeClass(class_list);
             }
         },
     
         update: function () {
             // the very first update seems to happen before the element is finished rendering
             // so we use setTimeout to give the element time to render
             var e = this.$el;
             var visible = this.model.get('visible');
             setTimeout(function() {e.toggle(visible)},0);
      
             var css = this.model.get('_css');
             if (css === undefined) {return;}
             for (var selector in css) {
                 if (css.hasOwnProperty(selector)) {
                     // Apply the css traits to all elements that match the selector.
                     var elements = this._get_selector_element(selector);
                     if (elements.length > 0) {
                         var css_traits = css[selector];    
                         for (var css_key in css_traits) {
                             if (css_traits.hasOwnProperty(css_key)) {
                                 elements.css(css_key, css_traits[css_key]);
                             }
                         }
                     }
                 }
             }
         },
 
         _get_selector_element: function (selector) {
             // Get the elements via the css selector.  If the selector is
             // blank, apply the style to the $el_to_style element.  If
             // the $el_to_style element is not defined, use apply the 
             // style to the view's element.
             var elements;
             if (selector === undefined || selector === null || selector === '') {
                 if (this.$el_to_style === undefined) {
                     elements = this.$el;
                 } else {
                     elements = this.$el_to_style;
                 }
             } else {
                 elements = this.$el.find(selector);
             }
             return elements;
         },
     });
 
     IPython.WidgetModel = WidgetModel;
     IPython.WidgetView = WidgetView;
     IPython.BaseWidgetView = BaseWidgetView;
 
     return widget_manager;
 });

IPython/html/widgets/widget.py

@@ -1,446 +1,450 b''
 """Base Widget class.  Allows user to create widgets in the backend that render
 in the IPython notebook frontend.
 """
 #-----------------------------------------------------------------------------
 # Copyright (c) 2013, the IPython Development Team.
 #
 # Distributed under the terms of the Modified BSD License.
 #
 # The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 from copy import copy
 from glob import glob
 import uuid
 import sys
 import os
 import inspect
 import types
 
 import IPython
 from IPython.kernel.comm import Comm
 from IPython.config import LoggingConfigurable
 from IPython.utils.traitlets import Unicode, Dict, List, Instance, Bool
 from IPython.display import Javascript, display
 from IPython.utils.py3compat import string_types
 
 from .widget_view import ViewWidget
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 
 class BaseWidget(LoggingConfigurable):
 
     # Shared declarations (Class level)
     _keys = List(Unicode, default_value = [], 
                  help="List of keys comprising the state of the model.", allow_none=False)
     widget_construction_callback = None
 
     def on_widget_constructed(callback):
         """Class method, registers a callback to be called when a widget is
         constructed.  The callback must have the following signature:
         callback(widget)"""
         BaseWidget.widget_construction_callback = callback
 
     def _handle_widget_constructed(widget):
         """Class method, called when a widget is constructed."""
         if BaseWidget.widget_construction_callback is not None and callable(BaseWidget.widget_construction_callback):
             BaseWidget.widget_construction_callback(widget)
 
     
 
     # Public declarations (Instance level)
     target_name = Unicode('widget', help="""Name of the backbone model 
         registered in the frontend to create and sync this widget with.""")
     default_view_name = Unicode(help="""Default view registered in the frontend
         to use to represent the widget.""")
 
     # Private/protected declarations
     # todo: change this to a context manager
     _property_lock = (None, None) # Last updated (key, value) from the front-end.  Prevents echo.
     _displayed = False
     _comm = Instance('IPython.kernel.comm.Comm')
     
     def __init__(self, **kwargs):
         """Public constructor
         """
         self._display_callbacks = []
         self._msg_callbacks = []
         super(BaseWidget, self).__init__(**kwargs)
 
         self.on_trait_change(self._handle_property_changed, self.keys)
         BaseWidget._handle_widget_constructed(self)
 
     def __del__(self):
         """Object disposal"""
         self.close()
 
 
     def close(self):
         """Close method.  Closes the widget which closes the underlying comm.
         When the comm is closed, all of the widget views are automatically
         removed from the frontend."""
         self._close_communication()
     
     
     # Properties
     @property
     def keys(self):
         keys = ['default_view_name']
         keys.extend(self._keys)
         return keys
     
     @property
     def comm(self):
         if self._comm is None:
             self._open_communication()
         return self._comm
 
+    @property
+    def model_id(self):
+        return self._comm.comm_id
+
     # Event handlers
     def _handle_msg(self, msg):
         """Called when a msg is recieved from the frontend"""
         data = msg['content']['data']
         method = data['method']
 
         # Handle backbone sync methods CREATE, PATCH, and UPDATE
         if method == 'backbone':
             if 'sync_method' in data and 'sync_data' in data:
                 sync_method = data['sync_method']
                 sync_data = data['sync_data']
                 self._handle_recieve_state(sync_data) # handles all methods
 
         # Handle a custom msg from the front-end
         elif method == 'custom':
             if 'custom_content' in data:
                 self._handle_custom_msg(data['custom_content'])
 
     def _handle_custom_msg(self, content):
         """Called when a custom msg is recieved."""
         for handler in self._msg_callbacks:
             if callable(handler):
                 argspec = inspect.getargspec(handler)
                 nargs = len(argspec[0])
 
                 # Bound methods have an additional 'self' argument
                 if isinstance(handler, types.MethodType):
                     nargs -= 1
 
                 # Call the callback
                 if nargs == 1:
                     handler(content)
                 elif nargs == 2:
                     handler(self, content)
                 else:
                     raise TypeError('Widget msg callback must ' \
                         'accept 1 or 2 arguments, not %d.' % nargs)
 
 
     def _handle_recieve_state(self, sync_data):
         """Called when a state is recieved from the frontend."""
         # Use _keys instead of keys - Don't get retrieve the css from the client side.
         for name in self._keys:
             if name in sync_data:
                 try:
                     self._property_lock = (name, sync_data[name])
                     setattr(self, name, sync_data[name])
                 finally:
                     self._property_lock = (None, None)
 
 
     def _handle_property_changed(self, name, old, new):
         """Called when a property has been changed."""
         # Make sure this isn't information that the front-end just sent us.
         if self._property_lock[0] != name and self._property_lock[1] != new:
             # Send new state to frontend
             self.send_state(key=name)
 
     def _handle_displayed(self, **kwargs):
         """Called when a view has been displayed for this widget instance
 
         Parameters
         ----------
         [view_name]: unicode (optional kwarg)
             Name of the view that was displayed."""
         for handler in self._display_callbacks:
             if callable(handler):
                 argspec = inspect.getargspec(handler)
                 nargs = len(argspec[0])
 
                 # Bound methods have an additional 'self' argument
                 if isinstance(handler, types.MethodType):
                     nargs -= 1
 
                 # Call the callback
                 if nargs == 0:
                     handler()
                 elif nargs == 1:
                     handler(self)
                 elif nargs == 2:
                     handler(self, kwargs.get('view_name', None))
                 else:
                     handler(self, **kwargs)
 
     # Public methods
     def send_state(self, key=None):
         """Sends the widget state, or a piece of it, to the frontend.
 
         Parameters
         ----------
         key : unicode (optional)
             A single property's name to sync with the frontend.
         """
         self._send({"method": "update",
                     "state": self.get_state()})
 
     def get_state(self, key=None):
         """Gets the widget state, or a piece of it.
 
         Parameters
         ----------
         key : unicode (optional)
             A single property's name to get.
         """
         state = {}
 
         # If a key is provided, just send the state of that key.
         if key is None:
             keys = self.keys[:]
         else:
             keys = [key]
         for k in keys:
             value = getattr(self, k)
 
             # a more elegant solution to encoding BaseWidgets would be
             # to tap into the JSON encoder and teach it how to deal
             # with BaseWidget objects, or maybe just teach the JSON
             # encoder to look for a _repr_json property before giving
             # up encoding
             if isinstance(value, BaseWidget):
-                value = value.comm.comm_id
+                value = value.model_id
             elif isinstance(value, list) and len(value)>0 and isinstance(value[0], BaseWidget):
                 # assume all elements of the list are widgets
-                value = [i.comm.comm_id for i in value]
+                value = [i.model_id for i in value]
             state[k] = value
         return state
 
 
     def send(self, content):
         """Sends a custom msg to the widget model in the front-end.
 
         Parameters
         ----------
         content : dict
             Content of the message to send.
         """
         self._send({"method": "custom",
                         "custom_content": content})
 
 
     def on_msg(self, callback, remove=False):
         """Register a callback for when a custom msg is recieved from the front-end
 
         Parameters
         ----------
         callback: method handler
             Can have a signature of:
             - callback(content)
             - callback(sender, content)
         remove: bool
             True if the callback should be unregistered."""
         if remove and callback in self._msg_callbacks:
             self._msg_callbacks.remove(callback)
         elif not remove and not callback in self._msg_callbacks:
             self._msg_callbacks.append(callback)
 
 
     def on_displayed(self, callback, remove=False):
         """Register a callback to be called when the widget has been displayed
 
         Parameters
         ----------
         callback: method handler
             Can have a signature of:
             - callback()
             - callback(sender)
             - callback(sender, view_name)
             - callback(sender, **kwargs)
               kwargs from display call passed through without modification.
         remove: bool
             True if the callback should be unregistered."""
         if remove and callback in self._display_callbacks:
             self._display_callbacks.remove(callback)
         elif not remove and not callback in self._display_callbacks:
             self._display_callbacks.append(callback)
 
 
     # Support methods
     def _repr_widget_(self, **kwargs):
         """Function that is called when `IPython.display.display` is called on
         the widget.
 
         Parameters
         ----------
         view_name: unicode (optional)
             View to display in the frontend.  Overrides default_view_name."""
         view_name = kwargs.get('view_name', self.default_view_name)
         
         # Create a communication.
         self._open_communication()
         
         # Make sure model is syncronized
         self.send_state()
             
         # Show view.
         self._send({"method": "display", "view_name": view_name})
         self._displayed = True
         self._handle_displayed(**kwargs)
 
 
     def _open_communication(self):
         """Opens a communication with the front-end."""
         # Create a comm.
         if self._comm is None:
             self._comm = Comm(target_name=self.target_name)
             self._comm.on_msg(self._handle_msg)
             self._comm.on_close(self._close_communication)
 
         # first update
         self.send_state()
 
 
     def _close_communication(self):
         """Closes a communication with the front-end."""
         if self._comm is not None:
             try:
                 self._comm.close()
             finally:
                 self._comm = None
 
 
     def _send(self, msg):
         """Sends a message to the model in the front-end"""
         if self._comm is not None:
             self._comm.send(msg)
             return True
         else:
             return False        
 
 class Widget(BaseWidget):
     visible = Bool(True, help="Whether or not the widget is visible.")
 
     # Private/protected declarations
     _css = Dict() # Internal CSS property dict
 
     # Properties
     @property
     def keys(self):
         keys = ['visible', '_css']
         keys.extend(super(Widget, self).keys)
         return keys
 
     def get_css(self, key, selector=""):
         """Get a CSS property of the widget.  Note, this function does not
         actually request the CSS from the front-end;  Only properties that have
         been set with set_css can be read.
 
         Parameters
         ----------
         key: unicode
             CSS key
         selector: unicode (optional)
             JQuery selector used when the CSS key/value was set.
         """
         if selector in self._css and key in self._css[selector]:
             return self._css[selector][key]
         else:
             return None
 
 
     def set_css(self, *args, **kwargs):
         """Set one or more CSS properties of the widget (shared among all of the
         views).  This function has two signatures:
         - set_css(css_dict, [selector=''])
         - set_css(key, value, [selector=''])
 
         Parameters
         ----------
         css_dict : dict
             CSS key/value pairs to apply
         key: unicode
             CSS key
         value
             CSS value
         selector: unicode (optional)
             JQuery selector to use to apply the CSS key/value.
         """
         selector = kwargs.get('selector', '')
 
         # Signature 1: set_css(css_dict, [selector=''])
         if len(args) == 1:
             if isinstance(args[0], dict):
                 for (key, value) in args[0].items():
                     self.set_css(key, value, selector=selector)
             else:
                 raise Exception('css_dict must be a dict.')
 
         # Signature 2: set_css(key, value, [selector=''])
         elif len(args) == 2 or len(args) == 3:
 
             # Selector can be a positional arg if it's the 3rd value
             if len(args) == 3:
                 selector = args[2]
             if selector not in self._css:
                 self._css[selector] = {}
 
             # Only update the property if it has changed.
             key = args[0]
             value = args[1]
             if not (key in self._css[selector] and value in self._css[selector][key]):
                 self._css[selector][key] = value
                 self.send_state('_css') # Send new state to client.
         else:
             raise Exception('set_css only accepts 1-3 arguments')
 
 
     def add_class(self, class_name, selector=""):
         """Add class[es] to a DOM element
 
         Parameters
         ----------
         class_name: unicode
             Class name(s) to add to the DOM element(s).  Multiple class names
             must be space separated.
         selector: unicode (optional)
             JQuery selector to select the DOM element(s) that the class(es) will
             be added to.
         """
         self.send({"msg_type": "add_class",
                    "class_list": class_name,
                    "selector": selector})
 
 
     def remove_class(self, class_name, selector=""):
         """Remove class[es] from a DOM element
 
         Parameters
         ----------
         class_name: unicode
             Class name(s) to remove from  the DOM element(s).  Multiple class
             names must be space separated.
         selector: unicode (optional)
             JQuery selector to select the DOM element(s) that the class(es) will
             be removed from.
         """
         self.send({"msg_type": "remove_class",
                    "class_list": class_name,
                    "selector": selector})
 
 
     def view(self, view_name=None):
         """Return a widget that can be displayed to display this widget using
         a non-default view"""
        return ViewWidget(self, view_name)