labeling.py

    reg = QgsGui.editorWidgetRegistry()
    if not EDITOR_WIDGET_REGISTRY_KEY in reg.factories().keys():
        factory = LabelShortcutWidgetFactory(EDITOR_WIDGET_REGISTRY_KEY)
        reg.registerWidget(EDITOR_WIDGET_REGISTRY_KEY, factory)
    else:
        labelEditorWidgetFactory = reg.factories()[EDITOR_WIDGET_REGISTRY_KEY]