Repository navigation
New site.py implementation fails to load .pth files in subprocesses #149819
Description
Activity
- changed the title [-]New site.py implementations fails fails to load .pth files in subprocesses[/-] [+]New site.py implementations fails to load .pth files in subprocesses[/+] on May 14, 2026
It works for me with the following test script.
#!/bin/sh # # Usage: # ./149819.sh # uses ./python.exe # ./149819.sh /usr/bin/python3 # uses a specific interpreter PYTHON=${1:-./python.exe} VENV=$(mktemp -d) "$PYTHON" -m venv "$VENV" SITE=$("$VENV"/bin/python -c 'import sysconfig; print(sysconfig.get_paths()["purelib"])') cat > "$SITE"/pp.pth <<EOF import sys; print('pp.pth') EOF "$VENV/bin/python" -c "import sys, subprocess; print('parent'); subprocess.run([sys.executable, '-c', 'print(\'child\')'])"
This outputs:
pp.pth parent pp.pth child
Closing as Can't Reproduce.
Closing as Can't Reproduce.
Don't expect everyone else to work 24/7 on fixing other people's code. :]
Here's the easy (for me) reproducer:
git clone https://github.com/cython/cython cd cython python3.16 -m venv venv . venv/bin/activate python3 -m pip install setuptools python3 runtests.py --debug "compile\.declarations"
Fails in a file that the test run generates with
Traceback (most recent call last): File "…/TEST_TMP/compile/declarations/setup.py", line 2, in <module> from distutils.core import setup ModuleNotFoundError: No module named 'distutils'I was using CPython's main branch at f1a47e7 for this (that's shortly after #149659 was merged).
Could you please try again with 87a879f from main or ad2f0cb from the 3.15 branch? I tried your recipe in both and it still WFM. It probably doesn't matter, but I'm on macOS.
% python3 runtests.py --debug "compile\.declarations" Python 3.15.0b1+ (heads/3.15:ad2f0cb997a, May 20 2026, 10:11:23) [Clang 21.0.0 (clang-2100.1.1.101)] Running tests against Cython 3.3.0a0 7eeaf92d5d0c5ee1c2964566856b4d0568e8532c Using Cython language level 2. Test dependency not found: 'numpy' Test dependency not found: 'pythran' Test dependency not found: 'setuptools.sandbox' Test dependency found: 'asyncio' version 3.15.0b1+ Test dependency found: 'pstats' version 3.15.0b1+ Test dependency found: 'posix' version 3.15.0b1+ Test dependency found: 'array' version ?.? Test dependency not found: 'Cython.Coverage' Test dependency not found: 'Cython.Coverage' Test dependency not found: 'IPython.testing.globalipapp' Test dependency not found: 'jedi_BROKEN_AND_DISABLED' Test dependency found: 'test.support' version 3.15.0b1+ Backends: c,cpp [etoe.declarations: SLOWTEST 0.88 sec] ---------------------------------------------------------------------- Ran 1 test in 0.888s OK Most expensive pipeline stages: 'AnalyseDeclarationsTransform': 0.15 / 8 (0.019 / run, 54.2%), 'parse': 0.03 / 8 (0.004 / run, 12.4%), 'generate_pyx_code_stage': 0.03 / 1 (0.031 / run, 11.1%), 'AnalyseExpressionsTransform': 0.01 / 8 (0.001 / run, 3.7%), 'PostParse': 0.01 / 8 (0.001 / run, 1.9%), 'OptimizeBuiltinCalls': 0.00 / 8 (0.001 / run, 1.6%), 'RemoveUnreachableCode': 0.00 / 16 (0.000 / run, 1.4%), 'InterpretCompilerDirectives': 0.00 / 8 (0.000 / run, 1.0%), 'MarkClosureVisitor': 0.00 / 8 (0.000 / run, 0.9%), 'ControlFlowAnalysis': 0.00 / 8 (0.000 / run, 0.9%) Times: etoe-build : 0.66 sec ( 1, 0.663 / run) - slowest: 'c:declarations(1)' (0.66s) etoe-run : 0.22 sec ( 1, 0.217 / run) - slowest: 'c:declarations(2)' (0.22s) ALL DONE
I tried with latest main (87a879f) and it fails for me, as before. This is on Ubuntu Linux. We don't have "latest main" integration tests running on anything else, so I can't compare right now. But your failure to reproduce it speaks for a platform specific issue. Possibly some spawn/fork/exec kind of difference?
- added a commit that references this issue on May 21, 2026
Please review the latest linked PR
Tried it, works for me, resolves this issue.
Reacted by tcely- changed the title [-]New site.py implementations fails to load .pth files in subprocesses[/-] [+]New site.py implementation fails to load .pth files in subprocesses[/+] on May 21, 2026
Fixed in main and 3.15 (it should show up in the next beta). Thanks again!
Reacted by tcely
Bug report
Bug description:
After #149583, .pth files are no longer loaded in Python subprocesses, as started with subprocess.run([sys.executable, …]) and the like.
The new implementation deliberately ignores .pth files in sys.path directories that are already known, and Python subprocesses already know all the paths of their parent process. Thus, all .pth files in those paths are ignored by subprocesses now.
I specifically noticed this when running setuptools in a build subprocess, which now fails to install its distutils replacement hack.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Linked PRs