Test if event has button attribute

Popup menu can be used with keyboard shortcut

tryton/gui/window/form.py

@@ -608,7 +608,7 @@ class Form(SignalEvent, TabContent):
 
     def _popup_menu_selected(self, menuitem, togglebutton, action, keyword):
         event = gtk.get_current_event()
-        if event.button == 1:
+        if not hasattr(event, 'button') or event.button == 1:
             hide = not bool(event.state
                 & (gtk.gdk.CONTROL_MASK | gtk.gdk.MOD1_MASK))
         else: