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fix(ci): prevent PYTHONHOME leak in Windows nox sub-sessions #559

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olivermeyer merged 1 commit into from
Apr 23, 2026
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fix(ci): prevent PYTHONHOME leak in Windows nox sub-sessions #559

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9 changes: 9 additions & 0 deletions noxfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -893,6 +893,15 @@ def _run_test_suite(session: nox.Session, marker: str = "", cov_append: bool = F
marker: Pytest marker expression
cov_append: Whether to append to existing coverage data
"""
# On Windows, uv run sets PYTHONHOME to the managed Python 3.14 install dir when it
# starts nox. This leaks into pytest sub-processes for older Python versions (3.11-3.13)
# and causes them to load Python 3.14's stdlib, crashing at startup.
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olivermeyer marked this conversation as resolved.
# Fix: set PYTHONHOME to None in session.env so nox strips it from the subprocess
# environment entirely (nox._clean_env filters out None-valued entries before passing
# to subprocess.Popen). Unlike os.environ.pop(), this does NOT mutate global process
# state; it only affects subprocesses spawned by session.run() / session.run_install().
if platform.system() == "Windows":
session.env["PYTHONHOME"] = None
_setup_venv(session)

posargs = session.posargs[:]
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