PyO3/pyo3 · error

Unrecognized TARGET environment variable value

Error message

Unrecognized TARGET environment variable value

What it means

Panic while parsing the TARGET environment variable into a Triple: the value exists but does not parse as a known Rust target triple (malformed, custom, or unsupported string), so the .parse().expect() aborts. The faulty input is the TARGET value itself as set by Cargo or the environment.

Solutions

1. Check the --target argument / TARGET value for typos or stray characters
2. Use a triple known to rustc (rustc --print target-list)
3. For custom targets, extend parsing in pyo3-build-config to recognize the triple

When it happens

Trigger: Thrown at pyo3-build-config/src/impl_.rs:74 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of PyO3/pyo3@ac9b6899d3 (2026-09-05). Data as JSON: /api/errors/656640409cfaf6a5. Report an issue: GitHub.

Appendix: source

Thrown at pyo3-build-config/src/impl_.rs:74

pub fn env_var(var: &str) -> Option<OsString> {
    println!("cargo:rerun-if-env-changed={var}");
    #[cfg(test)]
    {
        READ_ENV_VARS.with(|env_vars| {
            env_vars.borrow_mut().push(var.to_owned());
        });
    }
    env::var_os(var)
}

/// Gets the compilation target triple from environment variables set by Cargo.
///
/// Must be called from a crate build script.
pub fn target_triple_from_env() -> Triple {
    env::var("TARGET")
        .expect("target_triple_from_env() must be called from a build script")
        .parse()
        .expect("Unrecognized TARGET environment variable value")
}

fn sanitize_stable_abi_version(
    stable_abi_version: Option<PythonVersion>,
    version: PythonVersion,
) -> Result<PythonVersion> {
    if let Some(min_version) = stable_abi_version {
        ensure!(
            min_version <= version,
            "cannot set a minimum Python version {} higher than the interpreter version {} \
             (the minimum Python version is implied by the abi3-py3{} feature)",
            min_version,
            version,
            min_version.minor
        );
        Ok(min_version)
    } else {
        Ok(version)

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