pola-rs/polars · error

NAMED FUNCTION NOT FOUND

Error message

NAMED FUNCTION NOT FOUND

What it means

The registry is installed but get_function(&name, payload) returned None for the requested name: the serialized expression references a named column UDF that this process's registry does not know. The expect then panics with 'NAMED FUNCTION NOT FOUND'.

Source

Thrown at crates/polars-plan/src/dsl/expr/anonymous/expr.rs:184

    pub fn materialize(self) -> PolarsResult<SpecialEq<Arc<dyn AnonymousColumnsUdf>>> {
        match self {
            Self::Deserialized(t) => Ok(t),
            Self::Named {
                name,
                payload,
                value,
            } => feature_gated!("serde", {
                use super::named_serde::NAMED_SERDE_REGISTRY_EXPR;
                match value {
                    Some(v) => Ok(v),
                    None => Ok(SpecialEq(
                        NAMED_SERDE_REGISTRY_EXPR
                            .read()
                            .unwrap()
                            .as_ref()
                            .expect("NAMED EXPR REGISTRY NOT SET")
                            .get_function(&name, payload.unwrap().as_ref())
                            .expect("NAMED FUNCTION NOT FOUND"),
                    )),
                }
            }),
            Self::Bytes(_b) => {
                feature_gated!("serde";"python", {
                    serde_expr::deserialize_column_udf(_b.as_ref()).map(SpecialEq::new)
                })
            },
        }
    }
}

View on GitHub (pinned to df599052da)

Solutions

1. Register the named function in the consumer's ExprRegistry (exact name and payload format)
2. Verify producer and consumer agree on UDF names — treat UDF names as a compatibility contract
3. Load the owning plugin/extension before deserializing
4. If unknown names are expected, handle them before deserialization (e.g. inspect the payload) since the lookup currently panics rather than erroring

Example fix

// before: 'my_window_udf' unknown on consumer -> panic 'NAMED FUNCTION NOT FOUND'

// after: consumer registry maps every producer name
impl ExprRegistry for Reg {
    fn get_function(&self, name: &str, payload: &[u8]) -> Option<Arc<dyn AnonymousColumnsUdf>> {
        match name {
            "my_window_udf" => Some(Arc::new(MyWindowUdf::decode(payload))),
            _ => None,
        }
    }
}
set_named_serde_registry(Arc::new(Reg) as _);

for name in producer_function_names() {
    assert!(registry.get_function(name, &[]).is_some(), "function {name} not registered");
}

std::panic::catch_unwind(|| deserialize(bytes))
    .map_err(|_| format!("plan references a UDF unknown to this build"))

When it happens

Trigger: Consumer registry lacks the name the producer used — renamed/removed UDFs between versions, plugin not loaded, typo in the registered name, or a malicious/corrupted payload naming an arbitrary function.

Common situations: Version skew during rolling deploys, partial plugin installs, deserializing plans on machines that never loaded the extension providing the function.

Related errors

• NAMED AGG NOT FOUND
• NAMED EXPR REGISTRY NOT SET
• NAMED EXPR REGISTRY NOT SET
• not implemented
• not implemented

AI-assisted analysis of pola-rs/polars@df599052da (2026-08-16). Data as JSON: /api/errors/8edd73929f8e46d6. Report an issue: GitHub.