Alex Merose asked me on Mastodon how to best set up a conda environment on GitHub Actions. I thought I’d write a short blog post about it!

The short version is, use the conda-incubator/setup-miniconda GitHub action instead of the official setup-python action. Specifically, try out these options for size:

    - uses: conda-incubator/setup-miniconda@v2
        # Specify python version your environment will have. Remember to quote this, or
        # YAML will think you want python 3.1 not 3.10
        python-version: "3.10"
        # This uses *miniforge*, rather than *minicond*. The primary difference is that
        # the defaults channel is not enabled at all
        miniforge-version: latest
        # These properties enable the use of mamba, which is much faster and far less error
        # prone than conda while being completely compatible with the conda CLI
        use-mamba: true
        mamba-version: "*"

This should give you a python environment named test with python 3.10 (or whatever version you specify) and nothing much else. You can then use mamba to install packages from conda-forge to your heart’s content in future steps like this:

    - name: Install some packages
      # The `-l` is needed so conda environment activation works correctly
      shell: bash -l {0}
      run: |
                mamba install -c conda-forge numpy scipy matplotlib

My recommendation is to continue using the default setup-python action for almost all your python needs in GitHub actions, and use conda-incubator/setup-miniconda@v2 only if you explicitly need to use mamba (or conda) for something.