pola-rs/polars · error · ValueError

iceberg: unknown value for reader_override: '{reader_overrid

Error message

iceberg: unknown value for reader_override: '{reader_override}', expected one of ('native', 'pyiceberg')

What it means

Error "iceberg: unknown value for reader_override: '{reader_override}', expected one of ('native', 'pyiceberg')" thrown in pola-rs/polars.

Source

Thrown at py-polars/src/polars/io/iceberg/_dataset.py:356

            if verbose:
                eprint(
                    "IcebergScanResolver: to_dataset_scan(): early return "
                    f"({snapshot_id_key = })"
                )

            return None

        # Take from parameter first then envvar
        reader_override = self.reader_override or os.getenv(
            "POLARS_ICEBERG_READER_OVERRIDE"
        )

        if reader_override and reader_override not in ["native", "pyiceberg"]:
            msg = (
                "iceberg: unknown value for reader_override: "
                f"'{reader_override}', expected one of ('native', 'pyiceberg')"
            )
            raise ValueError(msg)

        fallback_reason = (
            "forced reader_override='pyiceberg'"
            if reader_override == "pyiceberg"
            else None
        )

        selected_fields = ("*",) if projection is None else tuple(projection)

        projected_iceberg_schema = (
            iceberg_schema
            if selected_fields == ("*",)
            else iceberg_schema.select(*selected_fields)
        )

        initial_defaults = {
            x: value
            for x in projected_iceberg_schema.field_ids

View on GitHub (pinned to df599052da)

When it happens

Trigger: Thrown at py-polars/src/polars/io/iceberg/_dataset.py:356 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/d06ffa22bb8a2b84. Report an issue: GitHub.