using nox and uv only to test multiple python versions

[bartdorlandt]

Hi,
I'm struggling to use a pure uv only environment that can use nox for multiple python versions...

Dockerfile

FROM ubuntu:24.04

ARG DEBIAN_FRONTEND=noninteractive
ENV TZ=Etc/GMT
ENV PATH="$PATH:/root/.local/bin"
ENV NOX_DEFAULT_VENV_BACKEND=uv
ARG VERSIONS="3.12 3.11 3.10 3.9"
COPY --from=ghcr.io/astral-sh/uv:latest /uv /bin/uv

RUN uv python install ${VERSIONS} && \
    uv tool install nox[uv]

RUN apt-get update -qy && apt-get upgrade -qy && \
    apt-get install -qy --no-install-recommends \
        ca-certificates curl gnupg2 git openssh-client

noxfile.py

"""noxfile."""
from nox import session

py_versions = ["3.12", "3.11"]

@session(python=py_versions)
def tests(session):
    session.install(".")
    session.install("pytest", "pytest-cov")
    session.run("pytest")

the uv python install 3.x doesn't create any shims (like you would have with pyenv), so they are not known to the shell with python3.11 ...
I can call nox from uv per python versions, which works, but kind of beats the point of nox.

uv run --python 3.11 nox -s tests
uv run --python 3.12 nox -s tests

For each of the command the other environment would be skipped. Example:

nox > Running session tests-3.11
nox > Missing interpreters will error by default on CI systems.
nox > Session tests-3.11 skipped: Python interpreter 3.11 not found.

(therefore not specifying the different python versions in the noxfile.)
Has anyone else played with this already? (and got it to work?)
My goal is to use versions installed by uv only and preferably have it run automatically against all desired python versions.

uv version: 0.3.3

[bartdorlandt]

Additional info.

Using a simpler noxfile:

"""noxfile."""
from nox import session

@session()
def tests(session):
    session.install(".",)
    session.install("pytest", "pytest-cov")
    session.run("pytest")

it will run fine, for the specifically requested python version.

root@69e959d9538c:/src# nox -s tests
nox > Running session tests
nox > Creating virtual environment (uv) using python in .nox/tests
nox > /root/.local/share/uv/tools/nox/bin/uv pip install .
nox > /root/.local/share/uv/tools/nox/bin/uv pip install pytest pytest-cov
nox > pytest
=================================================== test session starts ====================================================
platform linux -- Python 3.12.5, pytest-8.3.2, pluggy-1.5.0
rootdir: /src
configfile: pyproject.toml
plugins: cov-5.0.0
...

Using it specifying another version is working:

root@69e959d9538c:/src# uv run --python 3.11 nox -s tests
nox > Running session tests
nox > Creating virtual environment (uv) using python in .nox/tests
nox > uv pip install .
nox > uv pip install pytest pytest-cov
nox > pytest
=================================================== test session starts ====================================================
platform linux -- Python 3.11.9, pytest-8.3.2, pluggy-1.5.0
rootdir: /src
configfile: pyproject.toml
plugins: cov-5.0.0

[charliermarsh]

Need to find a minute to play around with this before giving a confident answer. In the meantime would love to hear from others.

[samypr100]

@henryiii might have ideas on the ideal way to do this using Nox with uv as he was the author of the integration of nox with uv

[dsully]

I have the same need to run against multiple versions of Python, but ones that are built "in-house".

Currently we're using tox to drive this as opposed to another tool wrapping tox:

[tox]
envlist = prepare,test3{10,11,12},ci
ignore_basepython_conflict = true

[testenv]
base_python = python3.10
...

[testenv:test310]
depends = prepare
commands =
    pytest test --cov src
    mypy --config-file tox.ini src
    ...

[testenv:test311]
depends = prepare
commands =
    pytest test --cov src

[testenv:test312]
depends = prepare
commands =
    pytest test --cov src

...

[wpk-nist-gov]

I ran into the same issue. In the meantime, I'm just adding the paths to uv pythons to the os.environ using the following:

def add_uv_to_environ() -> None:
    import os
    import subprocess
    from pathlib import Path

    path_to_uv_pythons = (
        subprocess.check_output(
            ["uv", "python", "dir"], env={"NO_COLOR": "1", **os.environ}
        )
        .decode()
        .strip()
    )
    paths_new = ":".join(map(str, Path(path_to_uv_pythons).glob("*/bin")))
    paths_old = os.environ["PATH"]
    os.environ["PATH"] = f"{paths_new}:{paths_old}"


add_uv_to_environ()


@nox.session
def test(session): 
...

Or as a bash script shim-uv

#!/usr/bin/env bash
p=$PATH
for k in "$(uv python dir)"/*/bin; do
    p="${k}:${p}"
done

PATH=$p "$@"

and run

shim-uv nox/tox ....