Method _regroup

lib/sqlalchemy/sql/selectable.py:7228–7242

(
        self,
        fn: Callable[[Select[Unpack[TupleAny]]], Select[Unpack[TupleAny]]],
    )

        return []

    def _regroup(
        self,
        fn: Callable[[Select[Unpack[TupleAny]]], Select[Unpack[TupleAny]]],
    ) -> ScalarSelect[Any]:

        assert isinstance(self.element, ScalarSelect)
        element = self.element.element
        if not isinstance(element, Select):
            raise exc.InvalidRequestError(
                "Can only apply this operation to a plain SELECT construct"
            )
        new_element = fn(element)

        return_value = new_element.scalar_subquery()
        return return_value

    def select(self) -> Select[bool]:
        r"""Return a SELECT of this :class:`_expression.Exists`.