fix: isolate script mode from inherited PYTHONPATH - #1157
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henryiii merged 3 commits intoAug 10, 2026
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August 9, 2026 11:05
The strip protects the installer and the re-exec'd Nox interpreter, but sessions must see the same environment as a NOX_SCRIPT_MODE=none run. Stash the value as NOX_OUTER_PYTHONPATH and restore it in the child. Assisted-by: ClaudeCode:claude-fable-5
A mismatched outer PYTHONHOME is fatal to any venv interpreter (Fatal Python error: Failed to import encodings module), and venv activate scripts unset it for the same reason. Assisted-by: ClaudeCode:claude-fable-5
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Fixes #1044.
Problem
I reproduced the failure by placing a second Nox distribution on the outer
PYTHONPATHand forcing a freshvirtualenvscript environment.run_script_mode()carried that path into both the dependency installer and the re-executed Nox process. Pip could therefore treat the outer Nox distribution as already installed, while the child process could resolve packages outside the script environment instead of using the dependencies installed there.Change
I remove
PYTHONPATHfrom the environment passed to the installer and the re-executed Nox process when the selected backend is sandboxed.The
nonebackend continues to inheritPYTHONPATH, preserving its existing non-isolated behavior.I also added:
nonebackends across both process handoffs;virtualenvscript environment.Tests
pytest tests/test__cli.py::test_run_script_mode_pythonpath_isolation tests/test_main.py::test_noxfile_script_mode— 3 passedpytest tests/test_main.py::test_noxfile_script_mode_url_req— 1 passedgit diff --checkpassed