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[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 5b55b50) Co-authored-by: Itamar Oren <itamarost@gmail.com>
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‎Lib/test/test_getpath.py‎

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@@ -475,6 +475,109 @@ def test_venv_symlink_with_misleading_landmarks_posix(self):
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actual = getpath(ns, expected)
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self.assertEqual(expected, actual)
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def test_venv_symlink_to_launcher_outside_runtime_posix(self):
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"Test a venv whose base executable resolves away from its stdlib."
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ns = MockPosixNamespace(
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argv0="/venv/bin/python",
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PREFIX="/usr",
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)
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ns.add_known_xfile("/out/launcher")
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ns.add_known_xfile("/runtime/bin/python")
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ns.add_known_link("/runtime/bin/python", "/out/launcher")
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ns.add_known_xfile("/venv/bin/python")
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ns.add_known_link("/venv/bin/python", "/runtime/bin/python")
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ns.add_known_file("/runtime/lib/python9.8/os.py")
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ns.add_known_dir("/runtime/lib/python9.8/lib-dynload")
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ns.add_known_file("/venv/pyvenv.cfg", [
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"home = /runtime/bin",
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])
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expected = dict(
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executable="/venv/bin/python",
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prefix="/venv",
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exec_prefix="/venv",
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base_executable="/out/launcher",
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base_prefix="/runtime",
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base_exec_prefix="/runtime",
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module_search_paths_set=1,
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module_search_paths=[
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"/runtime/lib/python98.zip",
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"/runtime/lib/python9.8",
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"/runtime/lib/python9.8/lib-dynload",
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],
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)
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actual = getpath(ns, expected)
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self.assertEqual(expected, actual)
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def test_venv_symlink_to_separate_exec_prefix_posix(self):
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"Test a venv whose base executable lives under a separate exec_prefix."
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ns = MockPosixNamespace(
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argv0="/venv/bin/python",
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PREFIX="/usr",
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EXEC_PREFIX="/usr",
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)
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ns.add_known_xfile("/exec/bin/python")
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ns.add_known_xfile("/runtime/bin/python")
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ns.add_known_link("/runtime/bin/python", "/exec/bin/python")
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ns.add_known_xfile("/venv/bin/python")
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ns.add_known_link("/venv/bin/python", "/runtime/bin/python")
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ns.add_known_file("/runtime/lib/python9.8/os.py")
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ns.add_known_dir("/exec/lib/python9.8/lib-dynload")
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ns.add_known_file("/venv/pyvenv.cfg", [
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"home = /runtime/bin",
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])
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expected = dict(
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executable="/venv/bin/python",
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prefix="/venv",
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exec_prefix="/venv",
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base_executable="/exec/bin/python",
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base_prefix="/runtime",
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base_exec_prefix="/exec",
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module_search_paths_set=1,
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module_search_paths=[
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"/runtime/lib/python98.zip",
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"/runtime/lib/python9.8",
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"/exec/lib/python9.8/lib-dynload",
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],
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)
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actual = getpath(ns, expected)
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self.assertEqual(expected, actual)
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def test_venv_separate_exec_prefix_with_misleading_home_posix(self):
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"Test that a stale lib-dynload near home does not override the base executable."
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ns = MockPosixNamespace(
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argv0="/venv/bin/python",
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PREFIX="/stdlib",
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EXEC_PREFIX="/build/exec",
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)
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ns.add_known_xfile("/exec/bin/python")
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ns.add_known_xfile("/public/bin/python")
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ns.add_known_link("/public/bin/python", "/exec/bin/python")
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ns.add_known_xfile("/venv/bin/python")
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ns.add_known_link("/venv/bin/python", "/public/bin/python")
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ns.add_known_file("/stdlib/lib/python9.8/os.py")
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ns.add_known_dir("/exec/lib/python9.8/lib-dynload")
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# An empty directory near the symlink must not win.
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ns.add_known_dir("/public/lib/python9.8/lib-dynload")
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ns.add_known_file("/venv/pyvenv.cfg", [
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"home = /public/bin",
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])
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expected = dict(
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executable="/venv/bin/python",
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prefix="/venv",
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exec_prefix="/venv",
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base_executable="/exec/bin/python",
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base_prefix="/stdlib",
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base_exec_prefix="/exec",
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module_search_paths_set=1,
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module_search_paths=[
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"/stdlib/lib/python98.zip",
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"/stdlib/lib/python9.8",
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"/exec/lib/python9.8/lib-dynload",
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],
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)
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actual = getpath(ns, expected)
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self.assertEqual(expected, actual)
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def test_venv_non_installed_zip_path_posix(self):
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"Test a venv created from non-installed python has correct zip path."""
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ns = MockPosixNamespace(

‎Misc/NEWS.d/next/Core_and_Builtins/2026-10-22-12-30-11.gh-issue-106045.fkMW34.rst‎

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Fix :mod:`venv` path discovery when the base executable resolves to a
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location outside the installation pointed to by the ``home`` key in
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``pyvenv.cfg``. The standard library is now found from ``home``, and
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extension modules from the resolved executable's installation, instead of
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falling back to the compiled-in prefix.

‎Modules/getpath.py‎

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@@ -232,6 +232,7 @@ def search_up(prefix, *landmarks, test=isfile):
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stdlib_dir_was_set_in_config = bool(stdlib_dir)
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real_executable_dir = None
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base_executable_dir = None
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platstdlib_dir = None
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stdlib_zip = None
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@@ -412,7 +413,17 @@ def search_up(prefix, *landmarks, test=isfile):
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if base_executable and isfile(base_executable):
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# Search relative to the resolved base executable rather
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# than the potentially external symlink in pyvenv.cfg.
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executable_dir = real_executable_dir = dirname(base_executable)
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# If nothing there locates a standard library (e.g. a
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# launcher binary stored outside the installation that
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# 'home' points into), keep searching from 'home'.
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# base_executable_dir is still used to find platform
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# dependent libraries (exec_prefix) in that case.
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base_executable_dir = dirname(base_executable)
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if (
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isfile(joinpath(base_executable_dir, BUILDDIR_TXT))
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or search_up(base_executable_dir, ZIP_LANDMARK, *STDLIB_LANDMARKS)
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):
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executable_dir = real_executable_dir = base_executable_dir
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# home key found; stop iterating over lines
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break
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@@ -622,6 +633,11 @@ def search_up(prefix, *landmarks, test=isfile):
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exec_prefix = prefix
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if not exec_prefix and prefix and isdir(joinpath(prefix, PLATSTDLIB_LANDMARK)):
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exec_prefix = prefix
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if not exec_prefix and base_executable_dir and base_executable_dir != executable_dir:
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# The venv's resolved base executable may live under a separate
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# exec_prefix (e.g. ./configure --exec-prefix) even when the
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# stdlib was found from 'home'.
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exec_prefix = search_up(base_executable_dir, PLATSTDLIB_LANDMARK, test=isdir)
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if not exec_prefix and executable_dir:
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exec_prefix = search_up(executable_dir, PLATSTDLIB_LANDMARK, test=isdir)
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if not exec_prefix and EXEC_PREFIX:

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