[Notifications] Fix unhandled TypeErrors on Python 3

- Notify requires GLib.Variant for set_hint
- Twisted defer.fail only accepts Exceptions.

Fixes: #3267

deluge/plugins/Notifications/deluge_notifications/gtkui.py

@@ -42,7 +42,7 @@ except ImportError:
 
 try:
     require_version('Notify', '0.7')
-    from gi.repository import Notify
+    from gi.repository import Notify, GLib
 except (ValueError, ImportError):
     POPUP_AVAILABLE = False
 else:
@@ -174,15 +174,17 @@ class GtkUiNotifications(CustomNotifications):
         if not self.config['popup_enabled']:
             return defer.succeed(_('Popup notification is not enabled.'))
         if not POPUP_AVAILABLE:
-            return defer.fail(_('libnotify is not installed'))
+            err_msg = _('libnotify is not installed')
+            log.warning(err_msg)
+            return defer.fail(ImportError(err_msg))
 
         if Notify.init('Deluge'):
             self.note = Notify.Notification.new(title, message, 'deluge-panel')
-            self.note.set_hint('desktop-entry', 'deluge')
+            self.note.set_hint('desktop-entry', GLib.Variant.new_string('deluge'))
             if not self.note.show():
                 err_msg = _('Failed to popup notification')
                 log.warning(err_msg)
-                return defer.fail(err_msg)
+                return defer.fail(Exception(err_msg))
         return defer.succeed(_('Notification popup shown'))
 
     def __play_sound(self, sound_path=''):
@@ -191,7 +193,7 @@ class GtkUiNotifications(CustomNotifications):
         if not SOUND_AVAILABLE:
             err_msg = _('pygame is not installed')
             log.warning(err_msg)
-            return defer.fail(err_msg)
+            return defer.fail(ImportError(err_msg))
 
         pygame.init()
         try:
@@ -203,7 +205,7 @@ class GtkUiNotifications(CustomNotifications):
         except pygame.error as ex:
             err_msg = _('Sound notification failed %s') % ex
             log.warning(err_msg)
-            return defer.fail(err_msg)
+            return defer.fail(ex)
         else:
             msg = _('Sound notification Success')
             log.info(msg)