PyO3/pyo3 · error

target_triple_from_env() must be called from a build script

Error message

target_triple_from_env() must be called from a build script

What it means

Panic in target_triple_from_env: the TARGET environment variable, which only Cargo sets when running a build script, is absent because std::env::var("TARGET") failed. The function is a build-script helper; calling it from a normal binary, test, or before Cargo exports TARGET hits this expect.

Source

Thrown at pyo3-build-config/src/impl_.rs:72

/// Gets an external environment variable, and registers the build script to rerun if
/// the variable changes.
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)

View on GitHub (pinned to ac9b6899d3)

Solutions

1. Call target_triple_from_env only from a crate's build.rs
2. If invoked outside Cargo, set TARGET manually to the desired triple (e.g. x86_64-unknown-linux-gnu)
3. Use the target_triple crate or restructure the code to receive the triple as a parameter

When it happens

Trigger: Thrown at pyo3-build-config/src/impl_.rs:72 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/6c01d2831bf9f53b. Report an issue: GitHub.