def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def draw(self, context):
        layout = self.layout

        userpref = context.user_preferences

        layout.prop(userpref, "active_section", expand=True)