Add button widget

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

@@ -0,0 +1,31 @@
+
+require(["notebook/js/widget"], function(){
+    
+    var ButtonWidgetModel = IPython.WidgetModel.extend({});
+    IPython.notebook.widget_manager.register_widget_model('ButtonWidgetModel', ButtonWidgetModel);
+
+    var ButtonView = IPython.WidgetView.extend({
+      
+        // Called when view is rendered.
+        render : function(){
+            var that = this;
+            this.$el = $("<button />")
+                .addClass('btn')
+                .click(function() {
+                    that.model.set('clicks', that.model.get('clicks') + 1)
+                });
+
+            this.update(); // Set defaults.
+        },
+        
+        // Handles: Backend -> Frontend Sync
+        //          Frontent -> Frontend Sync
+        update : function(){
+            this.$el.html(this.model.get('description'));
+        },
+        
+    });
+
+    IPython.notebook.widget_manager.register_widget_view('ButtonView', ButtonView);
+
+});

IPython/html/widgets/__init__.py

@@ -1,6 +1,7 @@
 from widget import Widget, init_widget_js
 
 from widget_bool import BoolWidget
+from widget_button import ButtonWidget
 from widget_container import ContainerWidget
 from widget_float import FloatWidget
 from widget_float_range import FloatRangeWidget

IPython/html/widgets/widget_button.py

@@ -0,0 +1,40 @@
+from base import Widget
+from IPython.utils.traitlets import Unicode, Bool, Int
+
+class ButtonWidget(Widget):
+    target_name = Unicode('ButtonWidgetModel')
+    default_view_name = Unicode('ButtonView')
+    _keys = ['clicks', 'description', 'disabled']
+    
+    clicks = Int(0)
+    description = Unicode('') # Description of the button (label).
+    disabled = Bool(False) # Enable or disable user changes
+    
+    _click_handlers = []
+
+    def handle_click(self, callback, remove=False):
+        if remove:
+            self._click_handlers.remove(callback)
+        else:
+            self._click_handlers.append(callback)
+
+    def _clicks_changed(self, name, old, new):
+        if new > old:
+            for handler in self._click_handlers:
+                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)
+                    else:
+                        raise TypeError('ButtonWidget click callback must ' \
+                            'accept 0 or 1 arguments.')
+