Method _set_with_polymorphic

lib/sqlalchemy/orm/mapper.py:1390–1427

(
        self, with_polymorphic: Optional[_WithPolymorphicArg]
    )

            )

    def _set_with_polymorphic(
        self, with_polymorphic: Optional[_WithPolymorphicArg]
    ) -> None:
        if with_polymorphic == "*":
            self.with_polymorphic = ("*", None)
        elif isinstance(with_polymorphic, (tuple, list)):
            if isinstance(with_polymorphic[0], (str, tuple, list)):
                self.with_polymorphic = cast(
                    """Tuple[
                        Union[
                            Literal["*"],
                            Sequence[Union["Mapper[Any]", Type[Any]]],
                        ],
                        Optional["FromClause"],
                    ]""",
                    with_polymorphic,
                )
            else:
                self.with_polymorphic = (with_polymorphic, None)
        elif with_polymorphic is not None:
            raise sa_exc.ArgumentError(
                f"Invalid setting for with_polymorphic: {with_polymorphic!r}"
            )
        else:
            self.with_polymorphic = None

        if self.with_polymorphic and self.with_polymorphic[1] is not None:
            self.with_polymorphic = (
                self.with_polymorphic[0],
                coercions.expect(
                    roles.StrictFromClauseRole,
                    self.with_polymorphic[1],
                    allow_select=True,
                ),
            )

        if self.configured:
            self._expire_memoizations()

    def _add_with_polymorphic_subclass(self, mapper):
        subcl = mapper.class_