perspective-dev/perspective · error

Expected PYTHON to be set in CONDA_BUILD environment, but…

Error message

Expected PYTHON to be set in CONDA_BUILD environment, but it isn't.  maturin will likely detect the wrong Python.

What it means

Build-time warning in the perspective-python conda build path: CONDA_BUILD=1 was detected but the PYTHON environment variable is unset, so maturin cannot be pointed at the conda-managed interpreter and may build against the wrong Python installation, producing an ABI-mismatched wheel.

Solutions

1. Set the PYTHON env var to the conda build's python executable path before invoking the build
2. Verify the conda recipe exports PYTHON (standard conda-build behavior) and that it isn't stripped in the build script
3. Check conda-build version; older versions handle PYTHON differently
4. Review the maturin invocation flags to confirm which interpreter gets targeted

When it happens

Trigger: Thrown at rust/perspective-python/build.mjs:91 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of perspective-dev/perspective@11c8238c0c (2026-09-09). Data as JSON: /api/errors/296faf6d35443cac. Report an issue: GitHub.

Appendix: source

Thrown at rust/perspective-python/build.mjs:91

    target = "--target=aarch64-apple-darwin";
} else if (process.env.PSP_ARCH === "x86_64" && process.platform === "linux") {
    target = "--target=x86_64-unknown-linux-gnu --compatibility manylinux_2_28";
} else if (process.env.PSP_ARCH === "aarch64" && process.platform === "linux") {
    target = "--target=aarch64-unknown-linux-gnu";
}

if (build_wheel) {
    if (!!process.env.PSP_BUILD_VERBOSE) {
        flags += " -vv";
    }

    if (process.env.CONDA_BUILD === "1") {
        console.log("Building with Conda flags and features");
        if (process.env.PYTHON) {
            console.log(`interpreter: ${process.env.PYTHON}`);
            flags += ` --interpreter=${process.env.PYTHON}`;
        } else {
            console.warn(
                "Expected PYTHON to be set in CONDA_BUILD environment, but it isn't.  maturin will likely detect the wrong Python.",
            );
        }
        // we need to generate proto.rs using conda's protoc, which is set in
        // the environment.  we use the unstable "versioned" python abi
        features.push(["generate-proto"]);
    } else {
        // standard for in-repo builds.  a different set will be standard in the sdist
        const standard_features = ["abi3", "generate-proto", "protobuf-src"];

        console.log("Building with standard flags and features");
        features.push(...standard_features);
    }

    execSync(
        `${emsdk_prefix}maturin build ${flags} --features=${features.join(",")} ${target}`,
        { stdio: "inherit", env },
    );

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