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Title: gh-149504: Fix re-entrancy bug when .pth/.start file invokes site.addsitedir() by warsaw · Pull Request #149659 · python/cpython · GitHub

Open Graph Title: gh-149504: Fix re-entrancy bug when .pth/.start file invokes site.addsitedir() by warsaw · Pull Request #149659 · python/cpython

X Title: gh-149504: Fix re-entrancy bug when .pth/.start file invokes site.addsitedir() by warsaw · Pull Request #149659 · python/cpython

Description: Fix site.addsitedir() to allow re-entrant calls from within startup files. Previously, a .pth file containing an import line that called site.addsitedir() (or a .start entry point doing the same) could crash with RuntimeError: dictionary changed size during iteration during site initialization, breaking tools such as uv run --with. mkdir -p /tmp/site-repro/root /tmp/site-repro/overlay printf 'import site; site.addsitedir("/tmp/site-repro/overlay")\n' > /tmp/site-repro/root/reenter.pth ./python.exe -S -c 'import site; site.addsitedir("/tmp/site-repro/root"); print("done")' prints "done" for me. uv run --python /Users/jelle/py/cpython/python.exe --with iniconfig python -c 'import iniconfig' does not crash. The implementation is more comprehensive than #149516 and is more inline with a suggestion @ncoghlan made on the original PR. Thanks @zsol for providing your PR. @JelleZijlstra please take a look. Issue: gh-149504

Open Graph Description: Fix site.addsitedir() to allow re-entrant calls from within startup files. Previously, a .pth file containing an import line that called site.addsitedir() (or a .start entry point doing the same) ...

X Description: Fix site.addsitedir() to allow re-entrant calls from within startup files. Previously, a .pth file containing an import line that called site.addsitedir() (or a .start entry point doing the same) ...

Opengraph URL: https://github.com/python/cpython/pull/149659

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gh-149504: Fix re-entrancy bug when .pth/.start file invokes site.addsitedir() https://github.com/python/cpython/pull/149659/files#top
Show all changes 9 commits https://github.com/python/cpython/pull/149659/files
7108fb7 Add re-entrant tests for gh-149504 warsaw May 11, 2026 https://github.com/python/cpython/pull/149659/commits/7108fb7024a7cc4ba785401b8cdfc9aab8999dde
aae5378 Add end-to-end integration test coverage warsaw May 11, 2026 https://github.com/python/cpython/pull/149659/commits/aae5378fc3095f127b69a623e761ae7b2b848326
dc96d5d Implement a state class to process .pth and .start files warsaw May 11, 2026 https://github.com/python/cpython/pull/149659/commits/dc96d5d726a9864eb871feb5a4b2a4989153722b
c6cfcb0 Add a blurb warsaw May 11, 2026 https://github.com/python/cpython/pull/149659/commits/c6cfcb03f80b563fdb40040b87c39eedafcf2b14
04b67f7 One small round of cleanup. warsaw May 11, 2026 https://github.com/python/cpython/pull/149659/commits/04b67f7d8e9752f11781c67f78cd766693d393f2
c38ec2b Merge branch 'main' into gh-149504 warsaw May 11, 2026 https://github.com/python/cpython/pull/149659/commits/c38ec2b268b1228acb3a706f6d3d057fbf258347
ea34446 Merge branch 'main' into gh-149504 warsaw May 11, 2026 https://github.com/python/cpython/pull/149659/commits/ea344462b0a5687f18d9bc83e9dc46d14211a4d1
558ece4 Merge branch 'main' into gh-149504 warsaw May 12, 2026 https://github.com/python/cpython/pull/149659/commits/558ece4be223242a69a397fda8a636e225624f3a
9c488d7 Merge branch 'main' into gh-149504 warsaw May 13, 2026 https://github.com/python/cpython/pull/149659/commits/9c488d71ccb4a0cd18a5043040a59f4ffb63fea3
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