Multiple python versions in one environment

Some tools are designed to have access to multiple python interpreters, and then create their own virtualenvs. Tox is a common example (although there are other ways to use tox in Actions). Less common, but my use case, is maturin https://github.com/PyO3/maturin , which is used to build rust crates with python bindings. It’s a lot quicker to do them all at once rather than in different jobs, as most of the compiled code is shared.

It would be helpful if setup-python allowed users to pass an array of python versions and installed all of them (which one takes python is up for debate, but python3.7, python3.8 etc should be fine).

[btcross26]

I was able to use the Miniconda action as shown below to accomplish the OP’s mention for tox with multiple Pythons in one invocation, where I am testing a Python library for 3.7, 3.8, and 3.9. Note the bash -l {0} is required for the Miniconda action to work properly across steps. Below, the testenv environment is automatically active at each step. Essentially, I just create the extra Python environments using conda and append the paths for the Python binaries in those environments to the PATH when running tox in the testing environment.

name: build_tests
on: [push]
jobs:
  build:
    strategy:
      matrix:
        os: [ubuntu-latest, macos-latest, windows-latest]
    name: Run tox build tests
    runs-on: ${{ matrix.os }}
    defaults:
      run:
        shell: bash -l {0}
    steps:
      - name: Setup repo
        uses: actions/checkout@v2
      - uses: conda-incubator/setup-miniconda@v2
        with:
          miniconda-version: latest
          python-version: 3.8
          activate-environment: testenv
          channels: conda-forge
      - name: Setup conda python environments
        run: |
          conda config --set always_yes yes --set changeps1 no
          conda install -q -c conda-forge tox
          conda create -q -n py37 python=3.7
          conda create -q -n py39 python=3.9
      - name: Run pytest
        env:
          TOXENV: py37,py38,py39
        run: |
          export PY37_PATH=$CONDA/envs/py37/bin
          export PY39_PATH=$CONDA/envs/py39/bin
          export PATH=$PATH:$PY37_PATH:$PY39_PATH
          tox
      - name: Run code checks
        if: ${{ matrix.os == 'ubuntu-latest' }}
        env:
          TOXENV: typing,pypi-description,manifest,precom
        run: tox

[AraHaan]

I would go for installing x86 and x64 python’s at same time as well, expecially if it means generating python c extension modules depending on the platform.