Method _str_dict

lib/sqlalchemy/engine/url.py:243–296

(
        cls,
        dict_: Optional[
            Union[
                Sequence[Tuple[str, Union[Sequence[str], str]]],
                Mapping[str, Union[Sequence[str], str]],
            ]
        ],
    )

    @classmethod
    def _str_dict(
        cls,
        dict_: Optional[
            Union[
                Sequence[Tuple[str, Union[Sequence[str], str]]],
                Mapping[str, Union[Sequence[str], str]],
            ]
        ],
    ) -> util.immutabledict[str, Union[Tuple[str, ...], str]]:
        if dict_ is None:
            return util.EMPTY_DICT

        @overload
        def _assert_value(
            val: str,
        ) -> str: ...

        @overload
        def _assert_value(
            val: Sequence[str],
        ) -> Union[str, Tuple[str, ...]]: ...

        def _assert_value(
            val: Union[str, Sequence[str]],
        ) -> Union[str, Tuple[str, ...]]:
            if isinstance(val, str):
                return val
            elif isinstance(val, collections_abc.Sequence):
                return tuple(_assert_value(elem) for elem in val)
            else:
                raise TypeError(
                    "Query dictionary values must be strings or "
                    "sequences of strings"
                )

        def _assert_str(v: str) -> str:
            if not isinstance(v, str):
                raise TypeError("Query dictionary keys must be strings")
            return v

        dict_items: Iterable[Tuple[str, Union[Sequence[str], str]]]
        if isinstance(dict_, collections_abc.Sequence):
            dict_items = dict_
        else:
            dict_items = dict_.items()

        return util.immutabledict(
            {
                _assert_str(key): _assert_value(
                    value,
                )
                for key, value in dict_items
            }
        )

    def set(
        self,