Repository: ray-project/ray
File: python/ray/data/namespace_expressions/list_namespace.py (Python)

Code before:
        """Slice each list.

        Args:
            start: Start index (inclusive). Defaults to 0.
            stop: Stop index (exclusive). Defaults to list length.
            step: Step size. Defaults to 1.

        Returns:
            UDFExpr that extracts a slice from each list.
        """
        # Return type is the same as the input list type
        return_dtype = self._expr.data_type

        @pyarrow_udf(return_dtype=return_dtype)
        def _list_slice(arr: pyarrow.Array) -> pyarrow.Array:
            return pc.list_slice(
                arr,
                start=0 if start is None else start,
                stop=stop,
                step=1 if step is None else step,
            )

        return _list_slice(self._expr)

    def sort(
        self, order: str = "ascending", null_placement: str = "at_end"
    ) -> "UDFExpr":
        """Sort the elements within each list.

        Args:
            order: Sorting order, must be ``\"ascending\"`` or ``\"descending\"``.
            null_placement: Placement for null values, ``\"at_start\"`` or ``\"at_end\"``.

        Returns:
            UDFExpr providing the sorted lists.
        """

        if order not in {"ascending", "descending"}:
            raise ValueError(
                "order must be either 'ascending' or 'descending', got " f"{order!r}"
            )
        if null_placement not in {"at_start", "at_end"}:
            raise ValueError(
                "null_placement must be 'at_start' or 'at_end', got "
                f"{null_placement!r}"
            )

        return_dtype = self._expr.data_type

        if hasattr(pc, "list_sort"):


Review comment (suggestion):
Please use `Literal[str]` and ensure to encompass the viable options for order and null_placement args based on pyarrow docs 

Code after:
        def _list_len(arr: pyarrow.Array) -> pyarrow.Array:
            return pc.list_value_length(arr)

        return _list_len(self._expr)

    def __getitem__(self, key: Union[int, slice]) -> "UDFExpr":
        """Get element or slice using bracket notation.

        Args:
            key: An integer for element access or slice for list slicing.

        Returns:
            UDFExpr that extracts the element or slice.

        Example:
            >>> col("items").list[0]      # Get first item  # doctest: +SKIP
            >>> col("items").list[1:3]    # Get slice [1, 3)  # doctest: +SKIP
            >>> col("items").list[-1]     # Get last item  # doctest: +SKIP
        """
        if isinstance(key, int):
            return self.get(key)
        elif isinstance(key, slice):
            return self.slice(key.start, key.stop, key.step)
        else:
            raise TypeError(
                f"List indices must be integers or slices, not {type(key).__name__}"
            )

    def get(self, index: int) -> "UDFExpr":
        """Get element at the specified index from each list.

        Args:
            index: The index of the element to retrieve. Negative indices are supported.

        Returns:
            UDFExpr that extracts the element at the given index.
        """
        # Infer return type from the list's value type
        return_dtype = DataType(object)  # fallback
        if self._expr.data_type.is_arrow_type():
            arrow_type = self._expr.data_type.to_arrow_dtype()
            if pyarrow.types.is_list(arrow_type) or pyarrow.types.is_large_list(
                arrow_type
            ):
                return_dtype = DataType.from_arrow(arrow_type.value_type)
            elif pyarrow.types.is_fixed_size_list(arrow_type):
                return_dtype = DataType.from_arrow(arrow_type.value_type)

        @pyarrow_udf(return_dtype=return_dtype)
        def _list_get(arr: pyarrow.Array) -> pyarrow.Array:
            return pc.list_element(arr, index)