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gh-149819: fix .pth and .start file processing in subprocess when inheriting PYTHONPATH - #150177
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After PR pythongh-149583 (Fix double evaluation of .pth and .site files in venvs), .pth files are no longer loaded in subprocesses started with subprocess.run([sys.executable, ...]). The root cause: main() seeds known_paths from removeduppaths() with all sys.path entries inherited from the parent process. addsitedir() then skips .pth processing for every directory already in known_paths. Fix: - main(): call removeduppaths() for dedup but start known_paths as a fresh empty set, so that addsitedir() processes .pth files in every site-packages directory regardless of inherited sys.path. - addsitedir(): move known_paths.add() before the sys.path.append and guard the append with 'sitedir not in sys.path' to avoid creating duplicate entries when called with a fresh known_paths. This preserves the pythongh-75723 dedup guarantee while allowing subprocesses to load .pth files.
* Extend _make_start() and _make_pth() to take an optional `basedir` which is used instead of `site.tmpdir` if given. * Add test_pth_processed_when_sitedir_already_on_path() to test the core GH#149819 bug: .pth files in subprocesses aren't handled if PYTHONPATH pointing to the .pth directory is inherited. * Similarly add test_start_processed_when_sitedir_already_on_path() to verify that .start files in the same circumstances are also now processed.
warsaw
commented
May 21, 2026
MemberAuthor
Also, reproducer by @tcely |
warsaw
commented
May 21, 2026
MemberAuthor
Also, original bug report by @scoder |
tcely
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May 21, 2026
This looks good to me. Thanks! |
scoder
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May 21, 2026
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scoder
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May 21, 2026
Contributor
Thanks for working on the site.py issues, BTW. That tends to be hairy business, regularly risking to break the setup of random people in some spot of the globe. I do appreciate it. |
Co-authored-by: scoder <stefan_ml@behnel.de>
warsaw
commented
May 21, 2026
MemberAuthor
And we had few core team members committed to maintaining site.py, but it seems like a natural place for me to get back involved in. Thank you both for engaging on this issue. I'm close to committing the branch. |
warsaw
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May 21, 2026 20:20
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Thanks @warsaw for the PR 🌮🎉.. I'm working now to backport this PR to: 3.15. |
GH-150202 is a backport of this pull request to the 3.15 branch. |
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May 21, 2026
…hen inheriting PYTHONPATH (GH-150177) (#150202) gh-149819: fix .pth and .start file processing in subprocess when inheriting PYTHONPATH (GH-150177) * gh-149819: Fix .pth files not loaded in Python subprocesses After PR gh-149583 (Fix double evaluation of .pth and .site files in venvs), .pth files are no longer loaded in subprocesses started with subprocess.run([sys.executable, ...]). The root cause: main() seeds known_paths from removeduppaths() with all sys.path entries inherited from the parent process. addsitedir() then skips .pth processing for every directory already in known_paths. Fix: - main(): call removeduppaths() for dedup but start known_paths as a fresh empty set, so that addsitedir() processes .pth files in every site-packages directory regardless of inherited sys.path. - addsitedir(): move known_paths.add() before the sys.path.append and guard the append with 'sitedir not in sys.path' to avoid creating duplicate entries when called with a fresh known_paths. This preserves the gh-75723 dedup guarantee while allowing subprocesses to load .pth files. * Fill out the tests for GH#149888 * Extend _make_start() and _make_pth() to take an optional `basedir` which is used instead of `site.tmpdir` if given. * Add test_pth_processed_when_sitedir_already_on_path() to test the core GH#149819 bug: .pth files in subprocesses aren't handled if PYTHONPATH pointing to the .pth directory is inherited. * Similarly add test_start_processed_when_sitedir_already_on_path() to verify that .start files in the same circumstances are also now processed. * Update Lib/site.py * Oops! Remove redundant code --------- (cherry picked from commit 3c298e2) Co-authored-by: Barry Warsaw <barry@python.org> Co-authored-by: BugBounty Mind <bugbounty-mind@deepseek.tui> Co-authored-by: scoder <stefan_ml@behnel.de>
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Followup to #149888 and #149819 - Fix by @IntentBug in the original PR, with test cases and review by @warsaw