Auto activate venv when python-version is set

[eifinger]

Closes: #124

[agriyakhetarpal]

Hi! I'm coming from #124 (comment), and I think this should resolve most of our problems with using setup-uv in pyodide/pyodide#5255.

However, additionally, I was also testing this action on HIPS/autograd#659, and I found that it was difficult to get uv to pick the correct Python version I have set up using the actions/setup-python action, and what this action is doing here seems to resolve the problem by using its own setup-python variable and using https://github.com/indygreg/python-build-standalone to grab Python binaries. Is there a way for uv to "infer" the version of Python I set using actions/setup-python without hacking my way with its outputs? That is, I'd love to be able to use the GHA Python builds seamlessly instead of using uv's Python builds, since the latter still have some rough edges when working with compiled projects – where building from source has been battle-tested on Python binaries from GHA (or other sources, such as conda-forge).

Edit: sorry, I should have checked the FAQ as well :) https://github.com/astral-sh/setup-uv#do-i-still-need-actionssetup-python-alongside-setup-uv. To elaborate a bit further: I think it's fine to use the standalone builds for pure Python projects and not recommend using actions/setup-python, but here was a recent case where there were troubles with NumPy: astral-sh/python-build-standalone#374

[eifinger]

@agriyakhetarpal I think the following should work:

test-python-version:
  runs-on: ubuntu-latest
    strategy:
      matrix:
        python-version: ["3.12", "3.13"]
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python
        with:
          python-version: ${{ matrix.python-version }}
      - name: Install latest version
        uses: astral-sh/setup-uv@auto-environment
        with:
          python-version: ${{ matrix.python-version }}

uv should then pickup the already configured system python by GHA and use it

[agriyakhetarpal]

Ah, good idea – I will try that after this PR makes it to a release, so that I don't need to pass --system to the install command. Thanks!

[ngoldbaum]

I should probably say that the weird floating point exception issues I saw with the python-build-standalone python I ultimately was able to reproduce with the python.org Python, so it probably has something to do with the system I was testing on.

The issues with INCLUDEPY should be resolved in uv.

I'm hoping to try converting some of the numpy and pyo3 CI jobs to use uv's python-build-standalone python soon and will follow up with any issues.

Thanks so much for working to improve Python packaging and distribution!