pola-rs/polars · error

can not get dtype of Enum AnyValue

Error message

can not get dtype of Enum AnyValue

What it means

Like Categorical, AnyValue::Enum/EnumOwned stores only the physical index and AnyValue::dtype() has no access to the Enum's ordered categories, so reconstructing DataType::Enum is impossible and the code panics with unimplemented!.

Solutions

1. Read the dtype from the Series (series.dtype()) rather than from the AnyValue.
2. Cast the series to String/Utf8 before extracting per-value data if you need the category text.
3. Match Enum variants explicitly in scalar code and consult the Enum's DataType (which you must hold alongside) for category info.
4. Skip Enum columns in generic scalar inspection code, treating them like Categorical.

Example fix

// before
let dtype = av.dtype(); // panics for Enum AnyValues
// after
let dtype = enum_series.dtype(); // DataType::Enum(categories, ordering)

fn scalar_dtype(av: &AnyValue) -> Option<DataType> {
    match av {
        AnyValue::Enum(..) | AnyValue::EnumOwned(..) => None,
        _ => Some(av.dtype()),
    }
}

if matches!(av, AnyValue::Enum(..) | AnyValue::EnumOwned(..)) { /* use series dtype */ }

When it happens

Trigger: Calling .dtype() on an AnyValue::Enum or AnyValue::EnumOwned, e.g. via get()/iter() on an Enum-typed series or via generic code paths that invoke dtype() on any extracted scalar.

Common situations: Working with DataType::Enum columns (fixed set of categories) and inspecting single values; generic scalar-processing helpers hitting Enum values at runtime.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• can not get dtype of Categorical AnyValue
• can't order enums from different FrozenCategories
• comparing enums with different FrozenCategories is not…
• invalid call to `get_strftime_format`; fmt=
• activate dtype

AI-assisted analysis of pola-rs/polars@fe841f959e (2026-09-18). Data as JSON: /api/errors/73c60a67a709a81f. Report an issue: GitHub.

Appendix: source

Thrown at crates/polars-core/src/datatypes/any_value.rs:255

            Binary(_) | BinaryOwned(_) => DataType::Binary,
            #[cfg(feature = "dtype-date")]
            Date(_) => DataType::Date,
            #[cfg(feature = "dtype-time")]
            Time(_) => DataType::Time,
            #[cfg(feature = "dtype-datetime")]
            Datetime(_, tu, tz) => DataType::Datetime(*tu, (*tz).cloned()),
            #[cfg(feature = "dtype-datetime")]
            DatetimeOwned(_, tu, tz) => {
                DataType::Datetime(*tu, tz.as_ref().map(|v| v.as_ref().clone()))
            },
            #[cfg(feature = "dtype-duration")]
            Duration(_, tu) => DataType::Duration(*tu),
            #[cfg(feature = "dtype-categorical")]
            Categorical(_, _) | CategoricalOwned(_, _) => {
                unimplemented!("can not get dtype of Categorical AnyValue")
            },
            #[cfg(feature = "dtype-categorical")]
            Enum(_, _) | EnumOwned(_, _) => unimplemented!("can not get dtype of Enum AnyValue"),
            List(s) => DataType::List(Box::new(s.dtype().clone())),
            #[cfg(feature = "dtype-map")]
            Map(s) => {
                let DataType::Struct(fields) = s.dtype() else {
                    unimplemented!("Map AnyValue payload must be a Struct")
                };
                DataType::Map(
                    Box::new(fields[0].dtype().clone()),
                    Box::new(fields[1].dtype().clone()),
                )
            },
            #[cfg(feature = "dtype-array")]
            Array(s, size) => DataType::Array(Box::new(s.dtype().clone()), *size),
            #[cfg(feature = "dtype-struct")]
            Struct(_, _, fields) => DataType::Struct(fields.to_vec()),
            #[cfg(feature = "dtype-struct")]
            StructOwned(payload) => DataType::Struct(payload.1.clone()),
            #[cfg(feature = "dtype-decimal")]

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