https://github.com/python/cpython/commit/522bc3dcbfa4b7adc44a1a01b5b51876d6a60b02
commit: 522bc3dcbfa4b7adc44a1a01b5b51876d6a60b02
branch: 3.15
author: Miss Islington (bot) <[email protected]>
committer: itamaro <[email protected]>
date: 2026-10-22T23:28:49Z
summary:
[3.15] gh-106045: Keep searching from venv home when the resolved base
executable has no stdlib (GH-160123) (#160354)
gh-106045: Keep searching from venv home when the resolved base executable has
no stdlib (GH-160123)
GH-156483 made `getpath` locate a venv's base installation relative to the
*resolved* base executable instead of the `home` key in `pyvenv.cfg`. When the
resolved executable lives outside the installation tree (e.g. a launcher binary
symlinked into it), nothing is found there and discovery falls back to the
compiled-in `PREFIX`. The venv then either fails to start or silently runs with
another installation's standard library.
This PR:
- Keeps GH-156483's behavior when the resolved executable's directory locates a
standard library (`pybuilddir.txt`, the stdlib zip, or `os.py`). Otherwise it
keeps searching from `home`, as before GH-156483.
- In that fallback case, still searches the resolved executable's directory for
`lib-dynload` when determining `exec_prefix`: after `prefix`, before `home` and
the compiled-in `EXEC_PREFIX`. Layouts with a separate exec prefix (e.g.
`./configure --exec-prefix`) then keep loading extension modules from the right
place, and a stale `lib-dynload` near the `home` symlink can't take precedence
over the one beside the resolved executable.
The tests added by GH-156483 pass unchanged. Three new `test_getpath` cases
cover the launcher-outside-the-installation and separate-exec-prefix layouts,
and a misleading `lib-dynload` near `home`; each fails without this change.
<details>
<summary>Reproducer</summary>
On `main` (0a86a34), with a plain `./configure --prefix=$HOME/py-under-test &&
make && make install`:
```sh
#!/bin/sh
# Usage: venv-home-repro.sh <installed-prefix> <X.Y>
set -eu
PREFIX=$1; VER=$2
W=$(mktemp -d)
mkdir -p "$W/runtime/bin" "$W/runtime/lib" "$W/launcher"
cp -R "$PREFIX/lib/python$VER" "$W/runtime/lib/"
cp "$PREFIX/bin/python$VER" "$W/launcher/python3"
ln -s "$W/launcher/python3" "$W/runtime/bin/python3"
PYTHONHOME="$W/runtime" "$W/runtime/bin/python3" -m venv --without-pip "$W/venv"
grep '^home' "$W/venv/pyvenv.cfg"
echo "expected base_prefix: $W/runtime"
"$W/venv/bin/python" -c 'import os, sys; print("actual base_prefix:",
sys.base_prefix); print("os.py loaded from:", os.__file__)'
```
Before:
```
home = /tmp/tmp.NFug9wEr4h/runtime/bin
expected base_prefix: /tmp/tmp.NFug9wEr4h/runtime
actual base_prefix: /home/user/py-under-test
os.py loaded from: /home/user/py-under-test/lib/python3.16/os.py
```
(With `$HOME/py-under-test/lib/python3.16` removed, the venv instead fails with
`ModuleNotFoundError: No module named 'encodings'`.)
After:
```
home = /tmp/tmp.8Zne2otFrw/runtime/bin
expected base_prefix: /tmp/tmp.8Zne2otFrw/runtime
actual base_prefix: /tmp/tmp.8Zne2otFrw/runtime
os.py loaded from: /tmp/tmp.8Zne2otFrw/runtime/lib/python3.16/os.py
```
</details>
(cherry picked from commit 5b55b502221b67660a4d652cdd3dd2203920e58a)
Co-authored-by: Itamar Oren <[email protected]>
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-10-22-12-30-11.gh-issue-106045.fkMW34.rst
M Lib/test/test_getpath.py
M Modules/getpath.py
diff --git a/Lib/test/test_getpath.py b/Lib/test/test_getpath.py
index 2907abe4b4cee6..abf8913cc950e8 100644
--- a/Lib/test/test_getpath.py
+++ b/Lib/test/test_getpath.py
@@ -475,6 +475,109 @@ def
test_venv_symlink_with_misleading_landmarks_posix(self):
actual = getpath(ns, expected)
self.assertEqual(expected, actual)
+ def test_venv_symlink_to_launcher_outside_runtime_posix(self):
+ "Test a venv whose base executable resolves away from its stdlib."
+ ns = MockPosixNamespace(
+ argv0="/venv/bin/python",
+ PREFIX="/usr",
+ )
+ ns.add_known_xfile("/out/launcher")
+ ns.add_known_xfile("/runtime/bin/python")
+ ns.add_known_link("/runtime/bin/python", "/out/launcher")
+ ns.add_known_xfile("/venv/bin/python")
+ ns.add_known_link("/venv/bin/python", "/runtime/bin/python")
+ ns.add_known_file("/runtime/lib/python9.8/os.py")
+ ns.add_known_dir("/runtime/lib/python9.8/lib-dynload")
+ ns.add_known_file("/venv/pyvenv.cfg", [
+ "home = /runtime/bin",
+ ])
+ expected = dict(
+ executable="/venv/bin/python",
+ prefix="/venv",
+ exec_prefix="/venv",
+ base_executable="/out/launcher",
+ base_prefix="/runtime",
+ base_exec_prefix="/runtime",
+ module_search_paths_set=1,
+ module_search_paths=[
+ "/runtime/lib/python98.zip",
+ "/runtime/lib/python9.8",
+ "/runtime/lib/python9.8/lib-dynload",
+ ],
+ )
+ actual = getpath(ns, expected)
+ self.assertEqual(expected, actual)
+
+ def test_venv_symlink_to_separate_exec_prefix_posix(self):
+ "Test a venv whose base executable lives under a separate exec_prefix."
+ ns = MockPosixNamespace(
+ argv0="/venv/bin/python",
+ PREFIX="/usr",
+ EXEC_PREFIX="/usr",
+ )
+ ns.add_known_xfile("/exec/bin/python")
+ ns.add_known_xfile("/runtime/bin/python")
+ ns.add_known_link("/runtime/bin/python", "/exec/bin/python")
+ ns.add_known_xfile("/venv/bin/python")
+ ns.add_known_link("/venv/bin/python", "/runtime/bin/python")
+ ns.add_known_file("/runtime/lib/python9.8/os.py")
+ ns.add_known_dir("/exec/lib/python9.8/lib-dynload")
+ ns.add_known_file("/venv/pyvenv.cfg", [
+ "home = /runtime/bin",
+ ])
+ expected = dict(
+ executable="/venv/bin/python",
+ prefix="/venv",
+ exec_prefix="/venv",
+ base_executable="/exec/bin/python",
+ base_prefix="/runtime",
+ base_exec_prefix="/exec",
+ module_search_paths_set=1,
+ module_search_paths=[
+ "/runtime/lib/python98.zip",
+ "/runtime/lib/python9.8",
+ "/exec/lib/python9.8/lib-dynload",
+ ],
+ )
+ actual = getpath(ns, expected)
+ self.assertEqual(expected, actual)
+
+ def test_venv_separate_exec_prefix_with_misleading_home_posix(self):
+ "Test that a stale lib-dynload near home does not override the base
executable."
+ ns = MockPosixNamespace(
+ argv0="/venv/bin/python",
+ PREFIX="/stdlib",
+ EXEC_PREFIX="/build/exec",
+ )
+ ns.add_known_xfile("/exec/bin/python")
+ ns.add_known_xfile("/public/bin/python")
+ ns.add_known_link("/public/bin/python", "/exec/bin/python")
+ ns.add_known_xfile("/venv/bin/python")
+ ns.add_known_link("/venv/bin/python", "/public/bin/python")
+ ns.add_known_file("/stdlib/lib/python9.8/os.py")
+ ns.add_known_dir("/exec/lib/python9.8/lib-dynload")
+ # An empty directory near the symlink must not win.
+ ns.add_known_dir("/public/lib/python9.8/lib-dynload")
+ ns.add_known_file("/venv/pyvenv.cfg", [
+ "home = /public/bin",
+ ])
+ expected = dict(
+ executable="/venv/bin/python",
+ prefix="/venv",
+ exec_prefix="/venv",
+ base_executable="/exec/bin/python",
+ base_prefix="/stdlib",
+ base_exec_prefix="/exec",
+ module_search_paths_set=1,
+ module_search_paths=[
+ "/stdlib/lib/python98.zip",
+ "/stdlib/lib/python9.8",
+ "/exec/lib/python9.8/lib-dynload",
+ ],
+ )
+ actual = getpath(ns, expected)
+ self.assertEqual(expected, actual)
+
def test_venv_non_installed_zip_path_posix(self):
"Test a venv created from non-installed python has correct zip path."""
ns = MockPosixNamespace(
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-10-22-12-30-11.gh-issue-106045.fkMW34.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-22-12-30-11.gh-issue-106045.fkMW34.rst
new file mode 100644
index 00000000000000..98abf1debe08d6
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-22-12-30-11.gh-issue-106045.fkMW34.rst
@@ -0,0 +1,5 @@
+Fix :mod:`venv` path discovery when the base executable resolves to a
+location outside the installation pointed to by the ``home`` key in
+``pyvenv.cfg``. The standard library is now found from ``home``, and
+extension modules from the resolved executable's installation, instead of
+falling back to the compiled-in prefix.
diff --git a/Modules/getpath.py b/Modules/getpath.py
index f5f928f1795de5..2ffb1d964c0fb6 100644
--- a/Modules/getpath.py
+++ b/Modules/getpath.py
@@ -232,6 +232,7 @@ def search_up(prefix, *landmarks, test=isfile):
stdlib_dir_was_set_in_config = bool(stdlib_dir)
real_executable_dir = None
+base_executable_dir = None
platstdlib_dir = None
stdlib_zip = None
@@ -412,7 +413,17 @@ def search_up(prefix, *landmarks, test=isfile):
if base_executable and isfile(base_executable):
# Search relative to the resolved base executable rather
# than the potentially external symlink in pyvenv.cfg.
- executable_dir = real_executable_dir =
dirname(base_executable)
+ # If nothing there locates a standard library (e.g. a
+ # launcher binary stored outside the installation that
+ # 'home' points into), keep searching from 'home'.
+ # base_executable_dir is still used to find platform
+ # dependent libraries (exec_prefix) in that case.
+ base_executable_dir = dirname(base_executable)
+ if (
+ isfile(joinpath(base_executable_dir, BUILDDIR_TXT))
+ or search_up(base_executable_dir, ZIP_LANDMARK,
*STDLIB_LANDMARKS)
+ ):
+ executable_dir = real_executable_dir =
base_executable_dir
# home key found; stop iterating over lines
break
@@ -622,6 +633,11 @@ def search_up(prefix, *landmarks, test=isfile):
exec_prefix = prefix
if not exec_prefix and prefix and isdir(joinpath(prefix,
PLATSTDLIB_LANDMARK)):
exec_prefix = prefix
+ if not exec_prefix and base_executable_dir and base_executable_dir !=
executable_dir:
+ # The venv's resolved base executable may live under a separate
+ # exec_prefix (e.g. ./configure --exec-prefix) even when the
+ # stdlib was found from 'home'.
+ exec_prefix = search_up(base_executable_dir, PLATSTDLIB_LANDMARK,
test=isdir)
if not exec_prefix and executable_dir:
exec_prefix = search_up(executable_dir, PLATSTDLIB_LANDMARK,
test=isdir)
if not exec_prefix and EXEC_PREFIX:
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