Some nox tests fails when PYTHONPATH is set #1044
Description
If you run nox tests with PYTHONPATH set and you do not have all dependencies installed locally then some tests could fail. In my case I do not have cowsay installed and when I do this:
/usr/bin/env -i \
PYTHONPATH=/data/builds/ul-workspace/components/python/nox/build/prototype/i386//usr/lib/python3.14/vendor-packages \
PATH=/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/bin:/usr/bin/amd64:/usr/bin:/usr/gnu/bin:/usr/sbin/amd64:/usr/sbin \
PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 \
/usr/bin/python3.14 -m pytest \
--color=no --cache-clear tests/test_main.py::test_noxfile_script_mode -vv
Then I see this failure:
___________________________ test_noxfile_script_mode ___________________________
monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7fffac93d9b0>
def test_noxfile_script_mode(monkeypatch: pytest.MonkeyPatch) -> None:
monkeypatch.delenv("NOX_SCRIPT_MODE", raising=False)
job = subprocess.run(
[
sys.executable,
"-m",
"nox",
"-f",
Path(RESOURCES) / "noxfile_script_mode.py",
"-s",
"example",
],
check=False,
capture_output=True,
text=True,
encoding="utf-8",
)
print(job.stdout)
print(job.stderr)
> assert job.returncode == 0
E assert 1 == 0
E + where 1 = CompletedProcess(args=['/usr/bin/python3.14', '-m', 'nox', '-f', PosixPath('/data/builds/ul-workspace/components/python/nox/build/amd64-3.14/tests/resources/noxfile_script_mode.py'), '-s', 'example'], returncode=1, stdout='Requirement already satisfied: nox in /data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages (2025.11.12)\nCollecting cowsay\n Using cached cowsay-6.1-py3-none-any.whl.metadata (5.6 kB)\nCollecting argcomplete<4,>=1.9.4 (from nox)\n Using cached argcomplete-3.6.3-py3-none-any.whl.metadata (16 kB)\nCollecting attrs>=24.1 (from nox)\n Using cached attrs-25.4.0-py3-none-any.whl.metadata (10 kB)\nCollecting colorlog<7,>=2.6.1 (from nox)\n Using cached colorlog-6.10.1-py3-none-any.whl.metadata (11 kB)\nCollecting dependency-groups>=1.1 (from nox)\n Using cached dependency_groups-1.3.1-py3-none-any.whl.metadata (2.3 kB)\nCollecting humanize>=4 (from nox)\n Using cached humanize-4.15.0-py3-none-any.whl.metadata (7.8 kB)\nCollecting packaging>=21 (from nox)\n Using cached packaging-25.0-py3-none-any.whl.metadata (3.3 kB)\nCollecting virtualenv>=20.15 (from nox)\n Using cached virtualenv-20.35.4-py3-none-any.whl.metadata (4.6 kB)\nCollecting distlib<1,>=0.3.7 (from virtualenv>=20.15->nox)\n Using cached distlib-0.4.0-py2.py3-none-any.whl.metadata (5.2 kB)\nCollecting filelock<4,>=3.12.2 (from virtualenv>=20.15->nox)\n Using cached filelock-3.20.1-py3-none-any.whl.metadata (2.1 kB)\nCollecting platformdirs<5,>=3.9.1 (from virtualenv>=20.15->nox)\n Using cached platformdirs-4.5.1-py3-none-any.whl.metadata (12 kB)\nUsing cached argcomplete-3.6.3-py3-none-any.whl (43 kB)\nUsing cached colorlog-6.10.1-py3-none-any.whl (11 kB)\nUsing cached cowsay-6.1-py3-none-any.whl (25 kB)\nUsing cached attrs-25.4.0-py3-none-any.whl (67 kB)\nUsing cached dependency_groups-1.3.1-py3-none-any.whl (8.7 kB)\nUsing cached humanize-4.15.0-py3-none-any.whl (132 kB)\nUsing cached packaging-25.0-py3-none-any.whl (66 kB)\nUsing cached virtualenv-20.35.4-py3-none-any.whl (6.0 MB)\nUsing cached distlib-0.4.0-py2.py3-none-any.whl (469 kB)\nUsing cached filelock-3.20.1-py3-none-any.whl (16 kB)\nUsing cached platformdirs-4.5.1-py3-none-any.whl (18 kB)\nInstalling collected packages: distlib, platformdirs, packaging, humanize, filelock, cowsay, colorlog, attrs, argcomplete, virtualenv, dependency-groups\n\nSuccessfully installed argcomplete-3.6.3 attrs-25.4.0 colorlog-6.10.1 cowsay-6.1 dependency-groups-1.3.1 distlib-0.4.0 filelock-3.20.1 humanize-4.15.0 packaging-25.0 platformdirs-4.5.1 virtualenv-20.35.4\n', stderr='nox > Creating virtual environment (virtualenv) using python3.14 in .nox/_nox_script_mode\nTraceback (most recent call last):\n File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386//usr/bin/nox", line 8, in <module>\n sys.exit(main())\n ~~~~^^\n File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/_cli.py", line 202, in nox_main\n _main(main_ep=True)\n ~~~~~^^^^^^^^^^^^^^\n File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/_cli.py", line 275, in _main\n exit_code = execute_workflow(args)\n File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/_cli.py", line 55, in execute_workflow\n return workflow.execute(\n ~~~~~~~~~~~~~~~~^\n global_config=args,\n ^^^^^^^^^^^^^^^^^^^\n ...<10 lines>...\n ),\n ^^\n )\n ^\n File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/workflow.py", line 61, in execute\n return_value = function_(*args, **kwargs)\n File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/tasks.py", line 138, in load_nox_module\n return _load_and_exec_nox_module(global_config)\n File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/tasks.py", line 83, in _load_and_exec_nox_module\n loader.exec_module(module)\n ~~~~~~~~~~~~~~~~~~^^^^^^^^\n File "<frozen importlib._bootstrap_external>", line 759, in exec_module\n File "<frozen importlib._bootstrap>", line 491, in _call_with_frames_removed\n File "/data/builds/ul-workspace/components/python/nox/build/amd64-3.14/tests/resources/noxfile_script_mode.py", line 5, in <module>\n import cowsay\nModuleNotFoundError: No module named \'cowsay\'\n').returncode
/data/builds/ul-workspace/components/python/nox/build/amd64-3.14/tests/test_main.py:1090: AssertionError
----------------------------- Captured stdout call -----------------------------
Requirement already satisfied: nox in /data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages (2025.11.12)
Collecting cowsay
Using cached cowsay-6.1-py3-none-any.whl.metadata (5.6 kB)
Collecting argcomplete<4,>=1.9.4 (from nox)
Using cached argcomplete-3.6.3-py3-none-any.whl.metadata (16 kB)
Collecting attrs>=24.1 (from nox)
Using cached attrs-25.4.0-py3-none-any.whl.metadata (10 kB)
Collecting colorlog<7,>=2.6.1 (from nox)
Using cached colorlog-6.10.1-py3-none-any.whl.metadata (11 kB)
Collecting dependency-groups>=1.1 (from nox)
Using cached dependency_groups-1.3.1-py3-none-any.whl.metadata (2.3 kB)
Collecting humanize>=4 (from nox)
Using cached humanize-4.15.0-py3-none-any.whl.metadata (7.8 kB)
Collecting packaging>=21 (from nox)
Using cached packaging-25.0-py3-none-any.whl.metadata (3.3 kB)
Collecting virtualenv>=20.15 (from nox)
Using cached virtualenv-20.35.4-py3-none-any.whl.metadata (4.6 kB)
Collecting distlib<1,>=0.3.7 (from virtualenv>=20.15->nox)
Using cached distlib-0.4.0-py2.py3-none-any.whl.metadata (5.2 kB)
Collecting filelock<4,>=3.12.2 (from virtualenv>=20.15->nox)
Using cached filelock-3.20.1-py3-none-any.whl.metadata (2.1 kB)
Collecting platformdirs<5,>=3.9.1 (from virtualenv>=20.15->nox)
Using cached platformdirs-4.5.1-py3-none-any.whl.metadata (12 kB)
Using cached argcomplete-3.6.3-py3-none-any.whl (43 kB)
Using cached colorlog-6.10.1-py3-none-any.whl (11 kB)
Using cached cowsay-6.1-py3-none-any.whl (25 kB)
Using cached attrs-25.4.0-py3-none-any.whl (67 kB)
Using cached dependency_groups-1.3.1-py3-none-any.whl (8.7 kB)
Using cached humanize-4.15.0-py3-none-any.whl (132 kB)
Using cached packaging-25.0-py3-none-any.whl (66 kB)
Using cached virtualenv-20.35.4-py3-none-any.whl (6.0 MB)
Using cached distlib-0.4.0-py2.py3-none-any.whl (469 kB)
Using cached filelock-3.20.1-py3-none-any.whl (16 kB)
Using cached platformdirs-4.5.1-py3-none-any.whl (18 kB)
Installing collected packages: distlib, platformdirs, packaging, humanize, filelock, cowsay, colorlog, attrs, argcomplete, virtualenv, dependency-groups
Successfully installed argcomplete-3.6.3 attrs-25.4.0 colorlog-6.10.1 cowsay-6.1 dependency-groups-1.3.1 distlib-0.4.0 filelock-3.20.1 humanize-4.15.0 packaging-25.0 platformdirs-4.5.1 virtualenv-20.35.4
nox > Creating virtual environment (virtualenv) using python3.14 in .nox/_nox_script_mode
Traceback (most recent call last):
File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386//usr/bin/nox", line 8, in <module>
sys.exit(main())
~~~~^^
File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/_cli.py", line 202, in nox_main
_main(main_ep=True)
~~~~~^^^^^^^^^^^^^^
File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/_cli.py", line 275, in _main
exit_code = execute_workflow(args)
File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/_cli.py", line 55, in execute_workflow
return workflow.execute(
~~~~~~~~~~~~~~~~^
global_config=args,
^^^^^^^^^^^^^^^^^^^
...<10 lines>...
),
^^
)
^
File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/workflow.py", line 61, in execute
return_value = function_(*args, **kwargs)
File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/tasks.py", line 138, in load_nox_module
return _load_and_exec_nox_module(global_config)
File "/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/lib/python3.14/vendor-packages/nox/tasks.py", line 83, in _load_and_exec_nox_module
loader.exec_module(module)
~~~~~~~~~~~~~~~~~~^^^^^^^^
File "<frozen importlib._bootstrap_external>", line 759, in exec_module
File "<frozen importlib._bootstrap>", line 491, in _call_with_frames_removed
File "/data/builds/ul-workspace/components/python/nox/build/amd64-3.14/tests/resources/noxfile_script_mode.py", line 5, in <module>
import cowsay
ModuleNotFoundError: No module named 'cowsay'
When I add .nox/_nox_script_mode/... to PYTHONPATH then the test pass. This works:
/usr/bin/env -i \
PYTHONPATH=/data/builds/ul-workspace/components/python/nox/build/prototype/i386//usr/lib/python3.14/vendor-packages:.nox/_nox_script_mode/lib/python3.14/site-packages \
PATH=/data/builds/ul-workspace/components/python/nox/build/prototype/i386/usr/bin:/usr/bin/amd64:/usr/bin:/usr/gnu/bin:/usr/sbin/amd64:/usr/sbin \
PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 \
/usr/bin/python3.14 -m pytest \
--color=no --cache-clear tests/test_main.py::test_noxfile_script_mode -vv