PyO3 on WSL using the wrong Python? Force the right interpreter with PYO3_PYTHON and VS Code

Troubleshooting PyO3 on WSL: fix builds that detect Python 3.6 by setting PYO3_PYTHON and syncing rust-analyzer env in VS Code. Rust links to Python 3.7+.

When integrating Rust with Python via PyO3 on WSL, the chosen interpreter can make or break your build. A common pitfall is that the build picks up an older Python, even if you think you’ve overridden it. On Windows 11 with a WSL Red Hat 8 environment, attempting to force Python 3.11 through PYTHON_SYS_EXECUTABLE may still result in Python 3.6 being used, which is below PyO3’s supported range and causes proc-macros to fail.

Problem

The setup attempts to point PyO3 at a newer interpreter by exporting an environment variable, yet the build continues to detect Python 3.6. The failure looks like this:

error: the configured Python interpreter version (3.6) is lower than PyO3's minimum supported version (3.7)

Problem example

Here’s a minimal illustration of the approach that didn’t work in this scenario: PYTHON_SYS_EXECUTABLE is set to a Python 3.11 path, but the build still resolves to 3.6.

export PYTHON_SYS_EXECUTABLE=/path/to/python311

Despite that, the build script for pyo3-ffi reports Python 3.6 and aborts.

What’s going on

Within WSL, rust-analyzer and cargo can end up with a different environment than your interactive shell, and PyO3 is strict about which interpreter it binds to. In practice, telling the toolchain exactly which Python binary to use and ensuring rust-analyzer inherits that setting resolves the mismatch. The error clearly indicates the detected interpreter is 3.6, while PyO3 requires at least 3.7.

Fix

Explicitly set the interpreter PyO3 should use by pointing to the target Python executable, such as the one inside your virtualenv. Persist it in your shell profile if helpful.

export PYO3_PYTHON=/home/youruser/.venv/bin/python

Make sure rust-analyzer sees the same environment inside VS Code. Add the following to your settings.json so the analysis process uses the intended interpreter:

"rust-analyzer.cargo.extraEnv": {
  "PYO3_PYTHON": "/home/youruser/.venv/bin/python"
}

Verify that the Python visible in your WSL session matches what you expect PyO3 to consume:

which python
python --version

If the environment changes don’t seem to take effect immediately, restart VS Code and, if necessary, the WSL session.

Why this matters

PyO3 binds against a specific Python and enforces a minimum version. If the build links to an older interpreter—like 3.6 in this case—proc-macro expansion and build scripts will fail early. Ensuring the toolchain consistently targets the same Python interpreter across your shell, cargo, and rust-analyzer eliminates these hard-to-trace breakages.

Takeaways

Pin the interpreter with PYO3_PYTHON and propagate that configuration to rust-analyzer via settings.json. Confirm the active interpreter within WSL using which and python --version, and don’t hesitate to restart the editor or WSL if changes don’t immediately apply. With the environment aligned, PyO3 stops reaching for Python 3.6 and the build proceeds against a supported version.