perspective-dev/perspective · error · ValueError

Unknown Polars type

Error message

Unknown Polars type '{dtype}'

What it means

polars_type_to_psp maps Polars dtypes to Perspective ColumnTypes; when a dtype falls outside the handled set (e.g. pl.List, pl.Struct, pl.Time, pl.Decimal, or Enum), no mapping exists and the virtual server cannot build the schema, so it raises. Generic sentinel ValueError raised by the converter.

Solutions

1. Cast unsupported columns before loading, e.g. df.with_columns(pl.col("c").cast(pl.Utf8))
2. Drop or exclude non-primitive columns (List/Struct) from the table
3. Extend polars_type_to_psp with a mapping for the missing dtype if it should be supported

When it happens

Trigger: Thrown at rust/perspective-python/perspective/virtual_servers/polars.py:317 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of perspective-dev/perspective@11c8238c0c (2026-09-09). Data as JSON: /api/errors/68579ae490628664. Report an issue: GitHub.

Appendix: source

Thrown at rust/perspective-python/perspective/virtual_servers/polars.py:317

def polars_type_to_psp(dtype):
    """Convert a Polars `dtype` to a Perspective `ColumnType`."""
    if dtype in (pl.Utf8, pl.String):
        return "string"
    if dtype == pl.Categorical:
        return "string"
    if dtype in (pl.Int8, pl.Int16, pl.Int32, pl.UInt8, pl.UInt16):
        return "integer"
    if dtype in (pl.Int64, pl.UInt64, pl.UInt32, pl.Float32, pl.Float64):
        return "float"
    if dtype == pl.Date:
        return "date"
    if dtype == pl.Boolean:
        return "boolean"
    if isinstance(dtype, pl.Datetime) or dtype == pl.Datetime:
        return "datetime"

    msg = f"Unknown Polars type '{dtype}'"
    raise ValueError(msg)


def apply_filters(df, filters):
    """Apply a list of filter configs to a DataFrame."""
    if not filters:
        return df

    mask = pl.lit(True)
    for filt in filters:
        col_name = filt[0]
        op = filt[1]
        value = filt[2] if len(filt) > 2 else None

        if value is None:
            continue

        col_expr = pl.col(col_name)
        if op == "==":

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