Add None as a widget visible value to allow for visiblity: hidden

Now, visible can have three values:
  * True - show the widget
  * False - hide the widget and collapse the empty space
  * None - hide the widget and show the empty space

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

@@ -1,679 +1,686 b''
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define(["widgets/js/manager",
         "underscore",
         "backbone",
         "jquery",
         "base/js/utils",
         "base/js/namespace",
 ], function(widgetmanager, _, Backbone, $, utils, IPython){
 
     var WidgetModel = Backbone.Model.extend({
         constructor: function (widget_manager, model_id, comm) {
             /**
              * Constructor
              *
              * Creates a WidgetModel instance.
              *
              * Parameters
              * ----------
              * widget_manager : WidgetManager instance
              * model_id : string
              *      An ID unique to this model.
              * comm : Comm instance (optional)
              */
             this.widget_manager = widget_manager;
             this.state_change = Promise.resolve();
             this._buffered_state_diff = {};
             this.pending_msgs = 0;
             this.msg_buffer = null;
             this.state_lock = null;
             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) {
             /**
              * Send a custom msg over the comm.
              */
             if (this.comm !== undefined) {
                 var data = {method: 'custom', content: content};
                 this.comm.send(data, callbacks);
                 this.pending_msgs++;
             }
         },
 
         _handle_comm_closed: function (msg) {
             /**
              * Handle when a widget is closed.
              */
             this.trigger('comm:close');
             this.stopListening();
             this.trigger('destroy', this);
             delete this.comm.model; // Delete ref so GC will collect widget model.
             delete this.comm;
             delete this.model_id; // Delete id from model so widget manager cleans up.
             for (var id in this.views) {
                 if (this.views.hasOwnProperty(id)) {
                     this.views[id].remove();
                 }
             }
         },
 
         _handle_comm_msg: function (msg) {
             /**
              * Handle incoming comm msg.
              */
             var method = msg.content.data.method;
             var that = this;
             switch (method) {
                 case 'update':
                     this.state_change = this.state_change.then(function() {
                         return that.set_state(msg.content.data.state);
                     }).catch(utils.reject("Couldn't process update msg for model id '" + String(that.id) + "'", true));
                     break;
                 case 'custom':
                     this.trigger('msg:custom', msg.content.data.content);
                     break;
                 case 'display':
                     this.widget_manager.display_view(msg, this);
                     break;
             }
         },
 
         set_state: function (state) {
             var that = this;
             // Handle when a widget is updated via the python side.
             return this._unpack_models(state).then(function(state) {
                 that.state_lock = state;
                 try {
                     WidgetModel.__super__.set.call(that, state);
                 } finally {
                     that.state_lock = null;
                 }
             }).catch(utils.reject("Couldn't set model state", true));
         },
 
         _handle_status: function (msg, callbacks) {
             /**
              * Handle status msgs.
              *
              * execution_state : ('busy', 'idle', 'starting')
              */
             if (this.comm !== undefined) {
                 if (msg.content.execution_state ==='idle') {
                     // Send buffer if this message caused another message to be
                     // throttled.
                     if (this.msg_buffer !== null &&
                         (this.get('msg_throttle') || 3) === 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 {
                         --this.pending_msgs;
                     }
                 }
             }
         },
 
         callbacks: function(view) {
             /**
              * Create msg callbacks for a comm msg.
              */
             var callbacks = this.widget_manager.callbacks(view);
 
             if (callbacks.iopub === undefined) {
                 callbacks.iopub = {};
             }
 
             var that = this;
             callbacks.iopub.status = function (msg) {
                 that._handle_status(msg, callbacks);
             };
             return callbacks;
         },
 
         set: function(key, val, options) {
             /**
              * Set a value.
              */
             var return_value = WidgetModel.__super__.set.apply(this, arguments);
 
             // Backbone only remembers the diff of the most recent set()
             // operation.  Calling set multiple times in a row results in a 
             // loss of diff information.  Here we keep our own running diff.
             this._buffered_state_diff = $.extend(this._buffered_state_diff, this.changedAttributes() || {});
             return return_value;
         },
 
         sync: function (method, model, options) {
             /**
              * Handle sync to the back-end.  Called when a model.save() is called.
              *
              * Make sure a comm exists.
              */
             var error = options.error || function() {
                 console.error('Backbone sync error:', arguments);
             };
             if (this.comm === undefined) {
                 error();
                 return false;
             }
 
             // Delete any key value pairs that the back-end already knows about.
             var attrs = (method === 'patch') ? options.attrs : model.toJSON(options);
             if (this.state_lock !== null) {
                 var keys = Object.keys(this.state_lock);
                 for (var i=0; i<keys.length; i++) {
                     var key = keys[i];
                     if (attrs[key] === this.state_lock[key]) {
                         delete attrs[key];
                     }
                 }
             }
 
             // Only sync if there are attributes to send to the back-end.
             attrs = this._pack_models(attrs);
             if (_.size(attrs) > 0) {
 
                 // If this message was sent via backbone itself, it will not
                 // have any callbacks.  It's important that we create callbacks
                 // so we can listen for status messages, etc...
                 var callbacks = options.callbacks || this.callbacks();
 
                 // Check throttle.
                 if (this.pending_msgs >= (this.get('msg_throttle') || 3)) {
                     // 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.
                     
                     // Combine updates if it is a 'patch' sync, otherwise replace updates
                     switch (method) {
                         case 'patch':
                             this.msg_buffer = $.extend(this.msg_buffer || {}, attrs);
                             break;
                         case 'update':
                         case 'create':
                             this.msg_buffer = attrs;
                             break;
                         default:
                             error();
                             return false;
                     }
                     this.msg_buffer_callbacks = callbacks;
 
                 } else {
                     // We haven't exceeded the throttle, send the message like 
                     // normal.
                     var data = {method: 'backbone', sync_data: attrs};
                     this.comm.send(data, callbacks);
                     this.pending_msgs++;
                 }
             }
             // Since the comm is a one-way communication, assume the message 
             // arrived.  Don't call success since we don't have a model back from the server
             // this means we miss out on the 'sync' event.
             this._buffered_state_diff = {};
         },
 
         save_changes: function(callbacks) {
             /**
              * Push this model's state to the back-end
              *
              * This invokes a Backbone.Sync.
              */
             this.save(this._buffered_state_diff, {patch: true, callbacks: callbacks});
         },
 
         _pack_models: function(value) {
             /**
              * Replace models with model ids recursively.
              */
             var that = this;
             var packed;
             if (value instanceof Backbone.Model) {
                 return "IPY_MODEL_" + value.id;
 
             } else if ($.isArray(value)) {
                 packed = [];
                 _.each(value, function(sub_value, key) {
                     packed.push(that._pack_models(sub_value));
                 });
                 return packed;
             } else if (value instanceof Date || value instanceof String) {
                 return value;
             } else if (value instanceof Object) {
                 packed = {};
                 _.each(value, function(sub_value, key) {
                     packed[key] = that._pack_models(sub_value);
                 });
                 return packed;
 
             } else {
                 return value;
             }
         },
 
         _unpack_models: function(value) {
             /**
              * Replace model ids with models recursively.
              */
             var that = this;
             var unpacked;
             if ($.isArray(value)) {
                 unpacked = [];
                 _.each(value, function(sub_value, key) {
                     unpacked.push(that._unpack_models(sub_value));
                 });
                 return Promise.all(unpacked);
             } else if (value instanceof Object) {
                 unpacked = {};
                 _.each(value, function(sub_value, key) {
                     unpacked[key] = that._unpack_models(sub_value);
                 });
                 return utils.resolve_promises_dict(unpacked);
             } else if (typeof value === 'string' && value.slice(0,10) === "IPY_MODEL_") {
                 // get_model returns a promise already
                 return this.widget_manager.get_model(value.slice(10, value.length));
             } else {
                 return Promise.resolve(value);
             }
         },
 
         on_some_change: function(keys, callback, context) {
             /**
              * on_some_change(["key1", "key2"], foo, context) differs from
              * on("change:key1 change:key2", foo, context).
              * If the widget attributes key1 and key2 are both modified, 
              * the second form will result in foo being called twice
              * while the first will call foo only once.
              */
             this.on('change', function() {
                 if (keys.some(this.hasChanged, this)) {
                     callback.apply(context);
                 }
             }, this);
 
        },
     });
     widgetmanager.WidgetManager.register_widget_model('WidgetModel', WidgetModel);
 
 
     var WidgetView = Backbone.View.extend({
         initialize: function(parameters) {
             /**
              * Public constructor.
              */
             this.model.on('change',this.update,this);
             this.options = parameters.options;
             this.id = this.id || utils.uuid();
             this.model.views[this.id] = this;
             this.on('displayed', function() { 
                 this.is_displayed = true; 
             }, this);
         },
 
         update: function(){
             /**
              * Triggered on model change.
              *
              * Update view to be consistent with this.model
              */
         },
 
         create_child_view: function(child_model, options) {
             /**
              * Create and promise that resolves to a child view of a given model
              */
             var that = this;
             options = $.extend({ parent: this }, options || {});
             return this.model.widget_manager.create_view(child_model, options).catch(utils.reject("Couldn't create child view"), true);
         },
 
         callbacks: function(){
             /**
              * Create msg callbacks for a comm msg.
              */
             return this.model.callbacks(this);
         },
 
         render: function(){
             /**
              * Render the view.
              *
              * By default, this is only called the first time the view is created
              */
         },
 
         show: function(){
             /**
              * Show the widget-area
              */
             if (this.options && this.options.cell &&
                 this.options.cell.widget_area !== undefined) {
                 this.options.cell.widget_area.show();
             }
         },
 
         send: function (content) {
             /**
              * Send a custom msg associated with this view.
              */
             this.model.send(content, this.callbacks());
         },
 
         touch: function () {
             this.model.save_changes(this.callbacks());
         },
 
         after_displayed: function (callback, context) {
             /**
              * Calls the callback right away is the view is already displayed
              * otherwise, register the callback to the 'displayed' event.
              */
             if (this.is_displayed) {
                 callback.apply(context);
             } else {
                 this.on('displayed', callback, context);
             }
         },
     });
 
 
     var DOMWidgetView = WidgetView.extend({
         initialize: function (parameters) {
             /**
              * Public constructor
              */
             DOMWidgetView.__super__.initialize.apply(this, [parameters]);
             this.on('displayed', this.show, this);
             this.model.on('change:visible', this.update_visible, this);
             this.model.on('change:_css', this.update_css, this);
 
             this.model.on('change:_dom_classes', function(model, new_classes) {
                 var old_classes = model.previous('_dom_classes');
                 this.update_classes(old_classes, new_classes);
             }, this);
 
             this.model.on('change:color', function (model, value) { 
                 this.update_attr('color', value); }, this);
 
             this.model.on('change:background_color', function (model, value) { 
                 this.update_attr('background', value); }, this);
 
             this.model.on('change:width', function (model, value) { 
                 this.update_attr('width', value); }, this);
 
             this.model.on('change:height', function (model, value) { 
                 this.update_attr('height', value); }, this);
 
             this.model.on('change:border_color', function (model, value) { 
                 this.update_attr('border-color', value); }, this);
 
             this.model.on('change:border_width', function (model, value) { 
                 this.update_attr('border-width', value); }, this);
 
             this.model.on('change:border_style', function (model, value) { 
                 this.update_attr('border-style', value); }, this);
 
             this.model.on('change:font_style', function (model, value) { 
                 this.update_attr('font-style', value); }, this);
 
             this.model.on('change:font_weight', function (model, value) { 
                 this.update_attr('font-weight', value); }, this);
 
             this.model.on('change:font_size', function (model, value) { 
                 this.update_attr('font-size', this._default_px(value)); }, this);
 
             this.model.on('change:font_family', function (model, value) { 
                 this.update_attr('font-family', value); }, this);
 
             this.model.on('change:padding', function (model, value) { 
                 this.update_attr('padding', value); }, this);
 
             this.model.on('change:margin', function (model, value) { 
                 this.update_attr('margin', this._default_px(value)); }, this);
 
             this.model.on('change:border_radius', function (model, value) { 
                 this.update_attr('border-radius', this._default_px(value)); }, this);
 
             this.after_displayed(function() {
                 this.update_visible(this.model, this.model.get("visible"));
                 this.update_classes([], this.model.get('_dom_classes'));
                 
                 this.update_attr('color', this.model.get('color'));
                 this.update_attr('background', this.model.get('background_color'));
                 this.update_attr('width', this.model.get('width'));
                 this.update_attr('height', this.model.get('height'));
                 this.update_attr('border-color', this.model.get('border_color'));
                 this.update_attr('border-width', this.model.get('border_width'));
                 this.update_attr('border-style', this.model.get('border_style'));
                 this.update_attr('font-style', this.model.get('font_style'));
                 this.update_attr('font-weight', this.model.get('font_weight'));
                 this.update_attr('font-size', this.model.get('font_size'));
                 this.update_attr('font-family', this.model.get('font_family'));
                 this.update_attr('padding', this.model.get('padding'));
                 this.update_attr('margin', this.model.get('margin'));
                 this.update_attr('border-radius', this.model.get('border_radius'));
 
                 this.update_css(this.model, this.model.get("_css"));
             }, this);
         },
 
         _default_px: function(value) {
             /**
              * Makes browser interpret a numerical string as a pixel value.
              */
             if (/^\d+\.?(\d+)?$/.test(value.trim())) {
                 return value.trim() + 'px';
             }
             return value;
         },
 
         update_attr: function(name, value) {
             /**
              * Set a css attr of the widget view.
              */
             this.$el.css(name, value);
         },
 
         update_visible: function(model, value) {
             /**
              * Update visibility
              */
-            this.$el.toggle(value);
+            switch(value) {
+                case null: // python None
+                    this.$el.show().css('visibility', 'hidden'); break;
+                case false:
+                    this.$el.hide(); break;
+                case true:
+                    this.$el.show().css('visibility', ''); break;
+            }
          },
 
         update_css: function (model, css) {
             /**
              * Update the css styling of this view.
              */
             var e = this.$el;
             if (css === undefined) {return;}
             for (var i = 0; i < css.length; i++) {
                 // Apply the css traits to all elements that match the selector.
                 var selector = css[i][0];
                 var elements = this._get_selector_element(selector);
                 if (elements.length > 0) {
                     var trait_key = css[i][1];
                     var trait_value = css[i][2];
                     elements.css(trait_key ,trait_value);
                 }
             }
         },
 
         update_classes: function (old_classes, new_classes, $el) {
             /**
              * Update the DOM classes applied to an element, default to this.$el.
              */
             if ($el===undefined) {
                 $el = this.$el;
             }
             _.difference(old_classes, new_classes).map(function(c) {$el.removeClass(c);})
             _.difference(new_classes, old_classes).map(function(c) {$el.addClass(c);})
         },
 
         update_mapped_classes: function(class_map, trait_name, previous_trait_value, $el) {
             /**
              * Update the DOM classes applied to the widget based on a single
              * trait's value.
              *
              * Given a trait value classes map, this function automatically
              * handles applying the appropriate classes to the widget element
              * and removing classes that are no longer valid.
              *
              * Parameters
              * ----------
              * class_map: dictionary
              *  Dictionary of trait values to class lists.
              *  Example:
              *      {
              *          success: ['alert', 'alert-success'],
              *          info: ['alert', 'alert-info'],
              *          warning: ['alert', 'alert-warning'],
              *          danger: ['alert', 'alert-danger']
              *      };
              * trait_name: string
              *  Name of the trait to check the value of.
              * previous_trait_value: optional string, default ''
              *  Last trait value
              * $el: optional jQuery element handle, defaults to this.$el
              *  Element that the classes are applied to.
              */
             var key = previous_trait_value;
             if (key === undefined) {
                 key = this.model.previous(trait_name);
             }
             var old_classes = class_map[key] ? class_map[key] : [];
             key = this.model.get(trait_name);
             var new_classes = class_map[key] ? class_map[key] : [];
 
             this.update_classes(old_classes, new_classes, $el || this.$el);
         },
         
         _get_selector_element: function (selector) {
             /**
              * Get the elements via the css selector.
              */
             var elements;
             if (!selector) {
                 elements = this.$el;
             } else {
                 elements = this.$el.find(selector).addBack(selector);
             }
             return elements;
         },
     });
 
 
     var ViewList = function(create_view, remove_view, context) {
         /**
          * - create_view and remove_view are default functions called when adding or removing views
          * - create_view takes a model and returns a view or a promise for a view for that model
          * - remove_view takes a view and destroys it (including calling `view.remove()`)
          * - each time the update() function is called with a new list, the create and remove
          *   callbacks will be called in an order so that if you append the views created in the
          *   create callback and remove the views in the remove callback, you will duplicate 
          *   the order of the list.
          * - the remove callback defaults to just removing the view (e.g., pass in null for the second parameter)
          * - the context defaults to the created ViewList.  If you pass another context, the create and remove
          *   will be called in that context.
          */
 
         this.initialize.apply(this, arguments);
     };
 
     _.extend(ViewList.prototype, {
         initialize: function(create_view, remove_view, context) {
             this.state_change = Promise.resolve();
             this._handler_context = context || this;
             this._models = [];
             this.views = [];
             this._create_view = create_view;
             this._remove_view = remove_view || function(view) {view.remove();};
         },
 
         update: function(new_models, create_view, remove_view, context) {
             /**
              * the create_view, remove_view, and context arguments override the defaults
              * specified when the list is created.
              * returns a promise that resolves after this update is done
              */
             var remove = remove_view || this._remove_view;
             var create = create_view || this._create_view;
             if (create === undefined || remove === undefined){
                 console.error("Must define a create a remove function");
             }
             var context = context || this._handler_context;
             var added_views = [];
             var that = this;
             this.state_change = this.state_change.then(function() {
                 var i;
                  // first, skip past the beginning of the lists if they are identical
                 for (i = 0; i < new_models.length; i++) {
                     if (i >= that._models.length || new_models[i] !== that._models[i]) {
                         break;
                     }
                 }
                 var first_removed = i;
                 // Remove the non-matching items from the old list.
                 for (var j = first_removed; j < that._models.length; j++) {
                     remove.call(context, that.views[j]);
                 }
 
                 // Add the rest of the new list items.
                 for (; i < new_models.length; i++) {
                     added_views.push(create.call(context, new_models[i]));
                 }
                 // make a copy of the input array
                 that._models = new_models.slice();
                 return Promise.all(added_views).then(function(added) {
                     Array.prototype.splice.apply(that.views, [first_removed, that.views.length].concat(added));
                     return that.views;
                 });
             });
             return this.state_change;
         },
 
         remove: function() {
             /**
              * removes every view in the list; convenience function for `.update([])`
              * that should be faster
              * returns a promise that resolves after this removal is done
              */
             var that = this;
             this.state_change = this.state_change.then(function() {
                 for (var i = 0; i < that.views.length; i++) {
                     that._remove_view.call(that._handler_context, that.views[i]);
                 }
                 that._models = [];
                 that.views = [];
             });
             return this.state_change;
         },
     });
 
     var widget = {
         'WidgetModel': WidgetModel,
         'WidgetView': WidgetView,
         'DOMWidgetView': DOMWidgetView,
         'ViewList': ViewList,
     };
 
     // For backwards compatability.
     $.extend(IPython, widget);
 
     return widget;
 });

IPython/html/widgets/widget.py

@@ -1,481 +1,481 b''
 """Base Widget class.  Allows user to create widgets in the back-end that render
 in the IPython notebook front-end.
 """
 #-----------------------------------------------------------------------------
 # 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 contextlib import contextmanager
 import collections
 
 from IPython.core.getipython import get_ipython
 from IPython.kernel.comm import Comm
 from IPython.config import LoggingConfigurable
 from IPython.utils.importstring import import_item
 from IPython.utils.traitlets import Unicode, Dict, Instance, Bool, List, \
     CaselessStrEnum, Tuple, CUnicode, Int, Set
 from IPython.utils.py3compat import string_types
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 class CallbackDispatcher(LoggingConfigurable):
     """A structure for registering and running callbacks"""
     callbacks = List()
     
     def __call__(self, *args, **kwargs):
         """Call all of the registered callbacks."""
         value = None
         for callback in self.callbacks:
             try:
                 local_value = callback(*args, **kwargs)
             except Exception as e:
                 ip = get_ipython()
                 if ip is None:
                     self.log.warn("Exception in callback %s: %s", callback, e, exc_info=True)
                 else:
                     ip.showtraceback()
             else:
                 value = local_value if local_value is not None else value
         return value
 
     def register_callback(self, callback, remove=False):
         """(Un)Register a callback
 
         Parameters
         ----------
         callback: method handle
             Method to be registered or unregistered.
         remove=False: bool
             Whether to unregister the callback."""
         
         # (Un)Register the callback.
         if remove and callback in self.callbacks:
             self.callbacks.remove(callback)
         elif not remove and callback not in self.callbacks:
             self.callbacks.append(callback)
 
 def _show_traceback(method):
     """decorator for showing tracebacks in IPython"""
     def m(self, *args, **kwargs):
         try:
             return(method(self, *args, **kwargs))
         except Exception as e:
             ip = get_ipython()
             if ip is None:
                 self.log.warn("Exception in widget method %s: %s", method, e, exc_info=True)
             else:
                 ip.showtraceback()
     return m
 
 
 def register(key=None):
     """Returns a decorator registering a widget class in the widget registry. 
     If no key is provided, the class name is used as a key. A key is
     provided for each core IPython widget so that the frontend can use
     this key regardless of the language of the kernel"""
     def wrap(widget):
         l = key if key is not None else widget.__module__ + widget.__name__
         Widget.widget_types[l] = widget
         return widget
     return wrap
 
 
 class Widget(LoggingConfigurable):
     #-------------------------------------------------------------------------
     # Class attributes
     #-------------------------------------------------------------------------
     _widget_construction_callback = None
     widgets = {}
     widget_types = {}
 
     @staticmethod
     def on_widget_constructed(callback):
         """Registers a callback to be called when a widget is constructed.
 
         The callback must have the following signature:
         callback(widget)"""
         Widget._widget_construction_callback = callback
 
     @staticmethod
     def _call_widget_constructed(widget):
         """Static method, called when a widget is constructed."""
         if Widget._widget_construction_callback is not None and callable(Widget._widget_construction_callback):
             Widget._widget_construction_callback(widget)
 
     @staticmethod
     def handle_comm_opened(comm, msg):
         """Static method, called when a widget is constructed."""
         widget_class = import_item(msg['content']['data']['widget_class'])
         widget = widget_class(comm=comm)
 
 
     #-------------------------------------------------------------------------
     # Traits
     #-------------------------------------------------------------------------
     _model_module = Unicode(None, allow_none=True, help="""A requirejs module name
         in which to find _model_name. If empty, look in the global registry.""")
     _model_name = Unicode('WidgetModel', help="""Name of the backbone model 
         registered in the front-end to create and sync this widget with.""")
     _view_module = Unicode(help="""A requirejs module in which to find _view_name.
         If empty, look in the global registry.""", sync=True)
     _view_name = Unicode(None, allow_none=True, help="""Default view registered in the front-end
         to use to represent the widget.""", sync=True)
     comm = Instance('IPython.kernel.comm.Comm')
     
     msg_throttle = Int(3, sync=True, help="""Maximum number of msgs the 
         front-end can send before receiving an idle msg from the back-end.""")
     
     version = Int(0, sync=True, help="""Widget's version""")
     keys = List()
     def _keys_default(self):
         return [name for name in self.traits(sync=True)]
     
     _property_lock = Tuple((None, None))
     _send_state_lock = Int(0)
     _states_to_send = Set(allow_none=False)
     _display_callbacks = Instance(CallbackDispatcher, ())
     _msg_callbacks = Instance(CallbackDispatcher, ())
     
     #-------------------------------------------------------------------------
     # (Con/de)structor
     #-------------------------------------------------------------------------
     def __init__(self, **kwargs):
         """Public constructor"""
         self._model_id = kwargs.pop('model_id', None)
         super(Widget, self).__init__(**kwargs)
 
         Widget._call_widget_constructed(self)
         self.open()
 
     def __del__(self):
         """Object disposal"""
         self.close()
 
     #-------------------------------------------------------------------------
     # Properties
     #-------------------------------------------------------------------------
 
     def open(self):
         """Open a comm to the frontend if one isn't already open."""
         if self.comm is None:
             args = dict(target_name='ipython.widget',
                         data={'model_name': self._model_name,
                               'model_module': self._model_module})
             if self._model_id is not None:
                 args['comm_id'] = self._model_id
             self.comm = Comm(**args)
 
     def _comm_changed(self, name, new):
         """Called when the comm is changed."""
         if new is None:
             return
         self._model_id = self.model_id
         
         self.comm.on_msg(self._handle_msg)
         Widget.widgets[self.model_id] = self
         
         # first update
         self.send_state()
 
     @property
     def model_id(self):
         """Gets the model id of this widget.
 
         If a Comm doesn't exist yet, a Comm will be created automagically."""
         return self.comm.comm_id
 
     #-------------------------------------------------------------------------
     # Methods
     #-------------------------------------------------------------------------
 
     def close(self):
         """Close method.
 
         Closes the underlying comm.
         When the comm is closed, all of the widget views are automatically
         removed from the front-end."""
         if self.comm is not None:
             Widget.widgets.pop(self.model_id, None)
             self.comm.close()
             self.comm = None
     
     def send_state(self, key=None):
         """Sends the widget state, or a piece of it, to the front-end.
 
         Parameters
         ----------
         key : unicode, or iterable (optional)
             A single property's name or iterable of property names to sync with the front-end.
         """
         self._send({
             "method" : "update",
             "state"  : self.get_state(key=key)
         })
 
     def get_state(self, key=None):
         """Gets the widget state, or a piece of it.
 
         Parameters
         ----------
         key : unicode or iterable (optional)
             A single property's name or iterable of property names to get.
         """
         if key is None:
             keys = self.keys
         elif isinstance(key, string_types):
             keys = [key]
         elif isinstance(key, collections.Iterable):
             keys = key
         else:
             raise ValueError("key must be a string, an iterable of keys, or None")
         state = {}
         for k in keys:
             f = self.trait_metadata(k, 'to_json', self._trait_to_json)
             value = getattr(self, k)
             state[k] = f(value)
         return state
 
     def set_state(self, sync_data):
         """Called when a state is received from the front-end."""
         for name in self.keys:
             if name in sync_data:
                 json_value = sync_data[name]
                 from_json = self.trait_metadata(name, 'from_json', self._trait_from_json)
                 with self._lock_property(name, json_value):
                     setattr(self, name, from_json(json_value))
     
     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", "content": content})
 
     def on_msg(self, callback, remove=False):
         """(Un)Register a custom msg receive callback.
 
         Parameters
         ----------
         callback: callable
             callback will be passed two arguments when a message arrives::
             
                 callback(widget, content)
             
         remove: bool
             True if the callback should be unregistered."""
         self._msg_callbacks.register_callback(callback, remove=remove)
 
     def on_displayed(self, callback, remove=False):
         """(Un)Register a widget displayed callback.
 
         Parameters
         ----------
         callback: method handler
             Must have a signature of::
             
                 callback(widget, **kwargs)
             
             kwargs from display are passed through without modification.
         remove: bool
             True if the callback should be unregistered."""
         self._display_callbacks.register_callback(callback, remove=remove)
 
     #-------------------------------------------------------------------------
     # Support methods
     #-------------------------------------------------------------------------
     @contextmanager
     def _lock_property(self, key, value):
         """Lock a property-value pair.
 
         The value should be the JSON state of the property.
 
         NOTE: This, in addition to the single lock for all state changes, is 
         flawed.  In the future we may want to look into buffering state changes 
         back to the front-end."""
         self._property_lock = (key, value)
         try:
             yield
         finally:
             self._property_lock = (None, None)
 
     @contextmanager
     def hold_sync(self):
         """Hold syncing any state until the context manager is released"""
         # We increment a value so that this can be nested.  Syncing will happen when
         # all levels have been released.
         self._send_state_lock += 1
         try:
             yield
         finally:
             self._send_state_lock -=1
             if self._send_state_lock == 0:
                 self.send_state(self._states_to_send)
                 self._states_to_send.clear()
 
     def _should_send_property(self, key, value):
         """Check the property lock (property_lock)"""
         to_json = self.trait_metadata(key, 'to_json', self._trait_to_json)
         if (key == self._property_lock[0]
             and to_json(value) == self._property_lock[1]):
             return False
         elif self._send_state_lock > 0:
             self._states_to_send.add(key)
             return False
         else:
             return True
     
     # Event handlers
     @_show_traceback
     def _handle_msg(self, msg):
         """Called when a msg is received from the front-end"""
         data = msg['content']['data']
         method = data['method']
         if not method in ['backbone', 'custom']:
             self.log.error('Unknown front-end to back-end widget msg with method "%s"' % method)
 
         # Handle backbone sync methods CREATE, PATCH, and UPDATE all in one.
         if method == 'backbone' and 'sync_data' in data:
             sync_data = data['sync_data']
             self.set_state(sync_data) # handles all methods
 
         # Handle a custom msg from the front-end
         elif method == 'custom':
             if 'content' in data:
                 self._handle_custom_msg(data['content'])
 
     def _handle_custom_msg(self, content):
         """Called when a custom msg is received."""
         self._msg_callbacks(self, content)
 
     def _notify_trait(self, name, old_value, new_value):
         """Called when a property has been changed."""
         # Trigger default traitlet callback machinery.  This allows any user
         # registered validation to be processed prior to allowing the widget
         # machinery to handle the state.
         LoggingConfigurable._notify_trait(self, name, old_value, new_value)
 
         # Send the state after the user registered callbacks for trait changes
         # have all fired (allows for user to validate values).
         if self.comm is not None and name in self.keys:
         # Make sure this isn't information that the front-end just sent us.
             if self._should_send_property(name, new_value):
                 # Send new state to front-end
                 self.send_state(key=name)
 
     def _handle_displayed(self, **kwargs):
         """Called when a view has been displayed for this widget instance"""
         self._display_callbacks(self, **kwargs)
 
     def _trait_to_json(self, x):
         """Convert a trait value to json
 
         Traverse lists/tuples and dicts and serialize their values as well.
         Replace any widgets with their model_id
         """
         if isinstance(x, dict):
             return {k: self._trait_to_json(v) for k, v in x.items()}
         elif isinstance(x, (list, tuple)):
             return [self._trait_to_json(v) for v in x]
         elif isinstance(x, Widget):
             return "IPY_MODEL_" + x.model_id
         else:
             return x # Value must be JSON-able
 
     def _trait_from_json(self, x):
         """Convert json values to objects
 
         Replace any strings representing valid model id values to Widget references.
         """
         if isinstance(x, dict):
             return {k: self._trait_from_json(v) for k, v in x.items()}
         elif isinstance(x, (list, tuple)):
             return [self._trait_from_json(v) for v in x]
         elif isinstance(x, string_types) and x.startswith('IPY_MODEL_') and x[10:] in Widget.widgets:
             # we want to support having child widgets at any level in a hierarchy
             # trusting that a widget UUID will not appear out in the wild
             return Widget.widgets[x[10:]]
         else:
             return x
 
     def _ipython_display_(self, **kwargs):
         """Called when `IPython.display.display` is called on the widget."""
         # Show view.
         if self._view_name is not None:
             self._send({"method": "display"})
             self._handle_displayed(**kwargs)
 
     def _send(self, msg):
         """Sends a message to the model in the front-end."""
         self.comm.send(msg)
 
 
 class DOMWidget(Widget):
-    visible = Bool(True, help="Whether the widget is visible.", sync=True)
+    visible = Bool(True, allow_none=True, help="Whether the widget is visible.  False collapses the empty space, while None preserves the empty space.", sync=True)
     _css = Tuple(sync=True, help="CSS property list: (selector, key, value)")
     _dom_classes = Tuple(sync=True, help="DOM classes applied to widget.$el.")
     
     width = CUnicode(sync=True)
     height = CUnicode(sync=True)
     padding = CUnicode(sync=True)
     margin = CUnicode(sync=True)
 
     color = Unicode(sync=True)
     background_color = Unicode(sync=True)
     border_color = Unicode(sync=True)
 
     border_width = CUnicode(sync=True)
     border_radius = CUnicode(sync=True)
     border_style = CaselessStrEnum(values=[ # http://www.w3schools.com/cssref/pr_border-style.asp
         'none', 
         'hidden', 
         'dotted', 
         'dashed', 
         'solid', 
         'double', 
         'groove', 
         'ridge', 
         'inset', 
         'outset', 
         'initial', 
         'inherit', ''],
         default_value='', sync=True)
 
     font_style = CaselessStrEnum(values=[ # http://www.w3schools.com/cssref/pr_font_font-style.asp
         'normal', 
         'italic', 
         'oblique', 
         'initial', 
         'inherit', ''], 
         default_value='', sync=True)
     font_weight = CaselessStrEnum(values=[ # http://www.w3schools.com/cssref/pr_font_weight.asp
         'normal', 
         'bold', 
         'bolder', 
         'lighter',
         'initial', 
         'inherit', ''] + [str(100 * (i+1)) for i in range(9)], 
         default_value='', sync=True)
     font_size = CUnicode(sync=True)
     font_family = Unicode(sync=True)
 
     def __init__(self, *pargs, **kwargs):
         super(DOMWidget, self).__init__(*pargs, **kwargs)
 
         def _validate_border(name, old, new):
             if new is not None and new != '':
                 if name != 'border_width' and not self.border_width:
                     self.border_width = 1
                 if name != 'border_style' and self.border_style == '':
                     self.border_style = 'solid'
         self.on_trait_change(_validate_border, ['border_width', 'border_style', 'border_color'])

examples/Interactive Widgets/Widget Styling.ipynb

@@ -1,752 +1,775 b''
 {
  "cells": [
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "[Index](Index.ipynb) - [Back](Widget Events.ipynb) - [Next](Custom Widget - Hello World.ipynb)"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "%%html\n",
     "<style>\n",
     ".example-container { background: #999999; padding: 2px; min-height: 100px; }\n",
     ".example-container.sm { min-height: 50px; }\n",
     ".example-box { background: #9999FF; width: 50px; height: 50px; text-align: center; vertical-align: middle; color: white; font-weight: bold; margin: 2px;}\n",
     ".example-box.med { width: 65px; height: 65px; }   \n",
     ".example-box.lrg { width: 80px; height: 80px; }   \n",
     "</style>"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "from IPython.html import widgets\n",
     "from IPython.display import display"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "# Widget Styling"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "## Basic styling"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "The widgets distributed with IPython can be styled by setting the following traits:\n",
     "\n",
     "- width  \n",
     "- height  \n",
     "- fore_color  \n",
     "- back_color  \n",
     "- border_color  \n",
     "- border_width  \n",
     "- border_style  \n",
     "- font_style  \n",
     "- font_weight  \n",
     "- font_size  \n",
     "- font_family  \n",
     "\n",
     "The example below shows how a `Button` widget can be styled:"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "button = widgets.Button(\n",
     "    description='Hello World!',\n",
     "    width=100, # Integers are interpreted as pixel measurements.\n",
     "    height='2em', # em is valid HTML unit of measurement.\n",
     "    color='lime', # Colors can be set by name,\n",
     "    background_color='#0022FF', # and also by color code.\n",
     "    border_color='red')\n",
     "display(button)"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "## Parent/child relationships"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "To display widget A inside widget B, widget A must be a child of widget B.  Widgets that can contain other widgets have a **`children` attribute**.  This attribute can be **set via a keyword argument** in the widget's constructor **or after construction**.  Calling display on an **object with children automatically displays those children**, too."
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "from IPython.display import display\n",
     "\n",
     "float_range = widgets.FloatSlider()\n",
     "string = widgets.Text(value='hi')\n",
     "container = widgets.Box(children=[float_range, string])\n",
     "\n",
     "container.border_color = 'red'\n",
     "container.border_style = 'dotted'\n",
     "container.border_width = 3\n",
     "display(container) # Displays the `container` and all of it's children."
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "### After the parent is displayed"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "Children **can be added to parents** after the parent has been displayed.  The **parent is responsible for rendering its children**."
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "container = widgets.Box()\n",
     "container.border_color = 'red'\n",
     "container.border_style = 'dotted'\n",
     "container.border_width = 3\n",
     "display(container)\n",
     "\n",
     "int_range = widgets.IntSlider()\n",
     "container.children=[int_range]"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "## Fancy boxes"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "If you need to display a more complicated set of widgets, there are **specialized containers** that you can use.  To display **multiple sets of widgets**, you can use an **`Accordion` or a `Tab` in combination with one `Box` per set of widgets** (as seen below).  The \"pages\" of these widgets are their children.  To set the titles of the pages, one must **call `set_title` after the widget has been displayed**."
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "### Accordion"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "name1 = widgets.Text(description='Location:')\n",
     "zip1 = widgets.BoundedIntText(description='Zip:', min=0, max=99999)\n",
     "page1 = widgets.Box(children=[name1, zip1])\n",
     "\n",
     "name2 = widgets.Text(description='Location:')\n",
     "zip2 = widgets.BoundedIntText(description='Zip:', min=0, max=99999)\n",
     "page2 = widgets.Box(children=[name2, zip2])\n",
     "\n",
     "accord = widgets.Accordion(children=[page1, page2])\n",
     "display(accord)\n",
     "\n",
     "accord.set_title(0, 'From')\n",
     "accord.set_title(1, 'To')"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "### TabWidget"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "name = widgets.Text(description='Name:')\n",
     "color = widgets.Dropdown(description='Color:', values=['red', 'orange', 'yellow', 'green', 'blue', 'indigo', 'violet'])\n",
     "page1 = widgets.Box(children=[name, color])\n",
     "\n",
     "age = widgets.IntSlider(description='Age:', min=0, max=120, value=50)\n",
     "gender = widgets.RadioButtons(description='Gender:', values=['male', 'female'])\n",
     "page2 = widgets.Box(children=[age, gender])\n",
     "\n",
     "tabs = widgets.Tab(children=[page1, page2])\n",
     "display(tabs)\n",
     "\n",
     "tabs.set_title(0, 'Name')\n",
     "tabs.set_title(1, 'Details')"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "### Popup"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "Unlike the other two special containers, the `Popup` is only **designed to display one set of widgets**.  The `Popup` can be used to **display widgets outside of the widget area**.  "
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "counter = widgets.IntText(description='Counter:')\n",
     "popup = widgets.Popup(children=[counter], description='Popup Demo', button_text='Popup Button')\n",
     "display(popup)"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "counter.value += 1"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "counter.value += 1"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "popup.close()"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "# Alignment"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "Most widgets have a **`description` attribute**, which allows a label for the widget to be defined.\n",
     "The label of the widget **has a fixed minimum width**.\n",
     "The text of the label is **always right aligned and the widget is left aligned**:"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "display(widgets.Text(description=\"a:\"))\n",
     "display(widgets.Text(description=\"aa:\"))\n",
     "display(widgets.Text(description=\"aaa:\"))"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "If a **label is longer** than the minimum width, the **widget is shifted to the right**:"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "display(widgets.Text(description=\"a:\"))\n",
     "display(widgets.Text(description=\"aa:\"))\n",
     "display(widgets.Text(description=\"aaa:\"))\n",
     "display(widgets.Text(description=\"aaaaaaaaaaaaaaaaaa:\"))"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "If a `description` is **not set** for the widget, the **label is not displayed**:"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "display(widgets.Text(description=\"a:\"))\n",
     "display(widgets.Text(description=\"aa:\"))\n",
     "display(widgets.Text(description=\"aaa:\"))\n",
     "display(widgets.Text())"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "## Flex boxes"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "Widgets can be aligned using the `FlexBox`, `HBox`, and `VBox` widgets."
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "### Application to widgets"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "Widgets display vertically by default:"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "buttons = [widgets.Button(description=str(i)) for i in range(3)]\n",
     "display(*buttons)"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "### Using hbox"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "To make widgets display horizontally, you need to **child them to a `HBox` widget**."
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "container = widgets.HBox(children=buttons)\n",
     "display(container)"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "By setting the width of the container to 100% and its `pack` to `center`, you can center the buttons."
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "container.width = '100%'\n",
     "container.pack = 'center'"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "## Visibility"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "Sometimes it is necessary to **hide or show widgets** in place, **without having to re-display** the widget.\n",
-    "The `visibility` property of widgets can be used to hide or show **widgets that have already been displayed** (as seen below)."
+    "The `visible` property of widgets can be used to hide or show **widgets that have already been displayed** (as seen below).  The `visible` property can be:\n",
+    "* `True` - the widget is displayed\n",
+    "* `False` - the widget is hidden, and the empty space where the widget would be is collapsed\n",
+    "* `None` - the widget is hidden, and the empty space where the widget would be is shown"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "string = widgets.Latex(value=\"Hello World!\")\n",
-    "display(string) "
+    "w1 = widgets.Latex(value=\"First line\")\n",
+    "w2 = widgets.Latex(value=\"Second line\")\n",
+    "w3 = widgets.Latex(value=\"Third line\")\n",
+    "display(w1, w2, w3)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "w2.visible=None"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "string.visible=False"
+    "w2.visible=False"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "string.visible=True"
+    "w2.visible=True"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {
     "slideshow": {
      "slide_type": "slide"
     }
    },
    "source": [
     "### Another example"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "In the example below, a form is rendered, which conditionally displays widgets depending on the state of other widgets.  Try toggling the student checkbox."
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "form = widgets.VBox()\n",
     "first = widgets.Text(description=\"First Name:\")\n",
     "last = widgets.Text(description=\"Last Name:\")\n",
     "\n",
     "student = widgets.Checkbox(description=\"Student:\", value=False)\n",
     "school_info = widgets.VBox(visible=False, children=[\n",
     "    widgets.Text(description=\"School:\"),\n",
     "    widgets.IntText(description=\"Grade:\", min=0, max=12)\n",
     "    ])\n",
     "\n",
     "pet = widgets.Text(description=\"Pet's Name:\")\n",
     "form.children = [first, last, student, school_info, pet]\n",
     "display(form)\n",
     "\n",
     "def on_student_toggle(name, value):\n",
     "    if value:\n",
     "        school_info.visible = True\n",
     "    else:\n",
     "        school_info.visible = False\n",
     "student.on_trait_change(on_student_toggle, 'value')\n"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
     "[Index](Index.ipynb) - [Back](Widget Events.ipynb) - [Next](Custom Widget - Hello World.ipynb)"
    ]
   }
  ],
  "metadata": {
   "cell_tags": [
    [
     "<None>",
     null
    ]
   ],
   "kernelspec": {
+   "display_name": "Python 2",
+   "name": "python2"
+  },
+  "language_info": {
    "codemirror_mode": {
-    "name": "python",
+    "name": "ipython",
     "version": 2
    },
-   "display_name": "Python 2",
-   "language": "python",
-   "name": "python2"
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.8"
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-  "signature": "sha256:8bb091be85fd5e7f76082b1b4b98cddec92a856334935ac2c702fe5ec03f6eff"
+  "signature": "sha256:198630bf2c2eb00401b60a395ebc75049099864b62f0faaf416da02f9808c40b"
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  "nbformat": 4,
  "nbformat_minor": 0
 }
  No newline at end of file