Method setdefault

src/werkzeug/datastructures/mixins.py:117–118

(self, key: t.Any, default: t.Any = None)

        return rv

    def setdefault(self, key: t.Any, default: t.Any = None) -> t.NoReturn:
        _immutable_error(self)

    def update(self, arg: t.Any, /, **kwargs: t.Any) -> t.NoReturn:
        _immutable_error(self)