pola-rs/polars · error · TypeError

expected file to be a `str` since partition-by is set

Error message

expected file to be a `str` since partition-by is set

What it means

Error "expected file to be a `str` since partition-by is set" thrown in pola-rs/polars.

Source

Thrown at py-polars/src/polars/dataframe/frame.py:4362

                    table=tbl,
                    root_path=file,
                    **(pyarrow_options or {}),
                )
            else:
                pa.parquet.write_table(
                    table=tbl,
                    where=file,
                    **(pyarrow_options or {}),
                )

            return

        target: str | Path | IO[bytes] | PartitionBy = file
        engine: EngineType = "streaming"
        if partition_by is not None:
            if not isinstance(file, str):
                msg = "expected file to be a `str` since partition-by is set"
                raise TypeError(msg)

            from polars.io.partition import PartitionBy

            target = PartitionBy(
                file,
                key=partition_by,
                approximate_bytes_per_file=partition_chunk_size_bytes,
            )

        from polars.lazyframe.opt_flags import QueryOptFlags

        self.lazy().sink_parquet(
            target,
            compression=compression,
            compression_level=compression_level,
            statistics=statistics,
            row_group_size=row_group_size,
            data_page_size=data_page_size,

View on GitHub (pinned to df599052da)

When it happens

Trigger: Thrown at py-polars/src/polars/dataframe/frame.py:4362 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of pola-rs/polars@df599052da (2026-08-16). Data as JSON: /api/errors/ae69d0756d36f4d7. Report an issue: GitHub.