pola-rs/polars · error

{dt:?} not impl

Error message

{dt:?} not impl

What it means

Formatting fallback in Series/DataType display: the DataType variant has no dedicated formatter implementation in fmt.rs, so its Debug representation is emitted with a 'not impl' marker. It signals a missing formatting branch for that dtype, not bad user data.

Source

Thrown at crates/polars-core/src/fmt.rs:463

                format_array!(
                    f,
                    self.binary_offset().unwrap(),
                    "binary[offset]",
                    self.name(),
                    "Series"
                )
            },
            #[cfg(feature = "dtype-map")]
            DataType::Map(_, _) => {
                let dt = format!("{}", self.dtype());
                format_array!(f, self.map().unwrap(), &dt, self.name(), "Series")
            },
            #[cfg(feature = "dtype-extension")]
            DataType::Extension(_, _) => {
                let dt = format!("{}", self.dtype());
                format_array!(f, self.ext().unwrap(), &dt, self.name(), "Series")
            },
            dt => panic!("{dt:?} not impl"),
        }
    }
}

impl Display for Series {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        Debug::fmt(self, f)
    }
}

impl Debug for DataFrame {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        Display::fmt(self, f)
    }
}
#[cfg(any(feature = "fmt", feature = "fmt_no_tty"))]
fn make_str_val(v: &str, truncate: usize, ellipsis: &String) -> String {
    let v_trunc = &v[..v

View on GitHub (pinned to 68506541d2)

Solutions

1. Formatting is not implemented for this dtype; cast the value to a displayable type (string/numeric) first.
2. Implement a custom Display path or convert the value before formatting.

When it happens

Trigger: This panic/expect fires when execution reaches an unguarded state described by: "{dt:?} not impl". Typical triggers: unsupported dtype or feature-gated code path reached at runtime, invalid user input or environment variable value, calling API methods in the wrong order or on mismatched types, or data (lengths, offsets, ranges) violating the function's preconditions.

Common situations: Encountered when input data or configuration does not meet the preconditions of the throwing code path ("{dt:?} not impl"). Common cases: missing Cargo feature flags, mismatched dtypes/lengths between arrays or series, out-of-range temporal values, malformed environment variables, or operations on unsupported/complex nested types.

AI-assisted analysis of pola-rs/polars@68506541d2 (2026-08-19). Data as JSON: /api/errors/fb9cf2a57f4a7e6f. Report an issue: GitHub.