pydantic/monty · info

u32 fits usize on supported targets

Error message

u32 fits usize on supported targets

What it means

Internal `expect` in `hex_encode` (binascii.hexlify): converts the `bytes_per_sep` magnitude from `u32` to `usize` after `unsigned_abs()`. On all supported platforms `usize` is at least 32 bits, so the conversion cannot fail. Not reachable through `binascii.hexlify` with any separator or `bytes_per_sep` value.

Source

Thrown at crates/monty/src/modules/binascii.rs:427

            HeapData::LongInt(long) => {
                // `&` on a `BigInt` is two's-complement, so this is Python's
                // own `value & 0xffffffff` for negatives as well.
                Ok((&long.0 & BigInt::from(u32::MAX)).to_u32().expect("masked below 2**32"))
            }
            _ => Err(ExcType::type_error_not_integer(&value.py_type_name(vm))),
        },
        _ => Err(ExcType::type_error_not_integer(&value.py_type_name(vm))),
    }
}

/// Encodes bytes as lowercase hex, inserting `sep` every `bytes_per_sep` bytes.
///
/// A positive `bytes_per_sep` groups from the right, so any short group leads;
/// a negative one groups from the left. Zero, or no separator, means none.
fn hex_encode(data: &[u8], sep: Option<u8>, bytes_per_sep: i32) -> Vec<u8> {
    let group = match sep {
        Some(_) if bytes_per_sep != 0 && !data.is_empty() => usize::try_from(bytes_per_sep.unsigned_abs())
            .expect("u32 fits usize on supported targets")
            .min(data.len()),
        // Without a separator, or with an empty input, emit one flat run.
        _ => data.len().max(1),
    };
    // Groups are measured from the right when positive, so the leading group
    // absorbs the remainder.
    let lead = if bytes_per_sep > 0 {
        match data.len() % group {
            0 => group,
            remainder => remainder,
        }
    } else {
        group
    };

    let mut out = Vec::with_capacity(data.len() * 2 + data.len() / group);
    for (index, byte) in data.iter().enumerate() {
        if let Some(sep) = sep

View on GitHub (pinned to adc986b362)

Solutions

1. No runtime action; the code already documents the platform assumption in the expect message.

When it happens

Trigger: Unreachable; would only matter on a hypothetical target where `usize` < 32 bits, or if `unsigned_abs()` were replaced with an unchecked cast.

Common situations: Contributor-only, e.g. platform-porting audits.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• one character
• gather commit frame id is not a GatherFuture
• gather item is not a Coroutine, ExternalFuture, or GatherFut
• Cannot get identity of Dereferenced object
• invalid ascii byte

AI-assisted analysis of pydantic/monty@adc986b362 (2026-09-13). Data as JSON: /api/errors/5d8015923d801891. Report an issue: GitHub.