Better user experience when kernel isn't found

IPython/html/services/sessions/handlers.py

@@ -56,7 +56,11 b' class SessionRootHandler(IPythonHandler):'
             try:
                 model = sm.create_session(name=name, path=path, kernel_name=kernel_name)
             except NoSuchKernel:
-                raise web.HTTPError(400, "No such kernel: %s" % kernel_name)
+                msg = ("The '%s' kernel is not available. Please pick another "
+                       "suitable kernel instead, or install that kernel." % kernel_name)
+                status_msg = 'Kernel not found'
+                msg = dict(full=msg, short=status_msg)
+                raise web.HTTPError(400, json.dumps(msg))
 
         location = url_path_join(self.base_url, 'api', 'sessions', model['id'])
         self.set_header('Location', url_escape(location))

IPython/html/static/notebook/js/notificationarea.js

@@ -185,32 +185,22 b' define(['
         });
 
         this.events.on('start_failed.Session',function (session, xhr, status, error) {
-            var msg = $('<div/>');
-            msg.append($('<div/>')
-                       .text('The kernel could not be started. This might ' +
-                             'happen if the notebook was previously run with a kernel ' +
-                             'that you do not have installed. Please choose a different kernel, ' +
-                             'or install the needed kernel and then refresh this page.')
-                       .css('margin-bottom', '1em'));
-
-            msg.append($('<div/>')
-                       .text('The exact error was:')
-                       .css('margin-bottom', '1em'));
-
-            msg.append($('<div/>')
-                       .attr('class', 'alert alert-danger')
-                       .attr('role', 'alert')
-                       .text(JSON.parse(status.responseText).message));
+            var msg = JSON.parse(status.responseJSON.message);
 
+            that.save_widget.update_document_title();
+            $kernel_ind_icon.attr('class','kernel_dead_icon').attr('title','Kernel Dead');
+            knw.danger(msg.short, undefined, function () {
             dialog.modal({
                 title: "Failed to start the kernel",
-                body : msg,
+                    body : msg.full,
                 keyboard_manager: that.keyboard_manager,
                 notebook: that.notebook,
                 buttons : {
                     "Ok": { class: 'btn-primary' }
                 }
             });
+                return false;
+            });
         });
 
         this.events.on('websocket_closed.Kernel', function (event, data) {

IPython/html/static/services/sessions/js/session.js

@@ -112,7 +112,6 b' define(['
 
     Session.prototype._handle_start_failure = function (xhr, status, error) {
         this.events.trigger('start_failed.Session', [this, xhr, status, error]);
-        this.events.trigger('status_dead.Kernel');
     };
     
     /**