pola-rs/polars · error · ValueError

cannot apply delta_table_version for table of type

Error message

cannot apply delta_table_version for table of type {data_source_format}

What it means

`scan_table` raises ValueError when `delta_table_version` is supplied for a table whose `data_source_format` is not Delta Lake. Version/time-travel reads are a Delta-specific feature; other formats (PARQUET, CSV, etc.) have no version history, so the parameter cannot be honored. The error names the actual format detected server-side.

Solutions

1. Remove `delta_table_version` for non-Delta tables, or scan the table without time travel
2. Check the table's format (e.g. via the Unity Catalog REST API / catalog explorer) before passing Delta options
3. Convert the table to Delta Lake if versioned reads are genuinely needed

Example fix

// before
lf = pl.scan_unity_catalog_table("cat", "sch", "tbl", delta_table_version=3)  # PARQUET table
// after
lf = pl.scan_unity_catalog_table("cat", "sch", "tbl")  # drop Delta-only option

info = client.get_table(catalog, ns, table)
if info.data_source_format != 'DELTA' and delta_table_version is not None:
    raise ValueError('delta_table_version only applies to DELTA tables')

def supports_delta_version(fmt: str) -> bool:
    return fmt.upper() == 'DELTA'

try:
    lf = client.scan_table(c, n, t, delta_table_version=ver)
except ValueError as e:
    if 'delta_table_version' in str(e):
        lf = client.scan_table(c, n, t)  # scan without time travel
    else:
        raise

When it happens

Trigger: Calling `client.scan_table(catalog, ns, table, delta_table_version=3)` (or the higher-level `pl.scan_unity_catalog_table(..., delta_table_version=n)`) where the table's format is e.g. PARQUET.

Common situations: Assuming every Unity Catalog table is a Delta table; pointing a Delta-specific option set at a plain external parquet table; drift where a table was converted from Delta to another format.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

• cannot apply delta_table_options for table of type
• a non-HTTPS workspace_url was given
• cannot override reserved namespace
• cannot use credential_provider when passing a DeltaTable…
• cannot use credential_provider when passing a DeltaTable…

AI-assisted analysis of pola-rs/polars@fe841f959e (2026-09-18). Data as JSON: /api/errors/01d30976c084337a. Report an issue: GitHub.

Appendix: source

Thrown at py-polars/src/polars/catalog/unity/client.py:274

        )

        if data_source_format in ["DELTA", "DELTASHARING"]:
            from polars.io.delta import scan_delta

            return scan_delta(
                storage_location,
                version=delta_table_version,
                delta_table_options=delta_table_options,
                storage_options=storage_options,
                credential_provider=credential_provider,
            )

        if delta_table_version is not None:
            msg = (
                "cannot apply delta_table_version for table of type "
                f"{data_source_format}"
            )
            raise ValueError(msg)

        if delta_table_options is not None:
            msg = (
                "cannot apply delta_table_options for table of type "
                f"{data_source_format}"
            )
            raise ValueError(msg)

        return wrap_ldf(
            self._client.scan_table(
                catalog_name,
                namespace,
                table_name,
                credential_provider=credential_provider,
                cloud_options=storage_options,
            )
        )

View on GitHub (pinned to fe841f959e)