setup-python with container not working

[tomhaber]

Description:
I'm trying to get the following to work, but it gives an error while creating the pip cache. It looks to me as if it's trying to run pip outside of the container with the path inside.

jobs:
  run:
    runs-on: Linux
    container: ghcr.io/iterative/cml:0-dvc3-base1
    steps:
      - uses: actions/checkout@v3
      - uses: iterative/setup-cml@v1
      
      - uses: actions/setup-python@v5
        with:
          python-version: '3.13'
          cache: 'pip' # caching pip dependencies
      # Install requirements
      - run: pip install -r requirements.txt

Action version:
2.325.0

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:
3.13, 3.12 but I don't believe it affects the problem

Expected behavior:
Have it run successfully within the container

Actual behavior:
Seems to run pip cache outside of the container with the inside path?

[gowridurgad]

Hi @tomhaber,
Thank you for creating this issue. We will investigate it and provide feedback as soon as we have some updates.

[tomhaber]

I'm happy to run additional tests if needed or alternative approaches

[aparnajyothi-y]

Hi @tomhaber, The error mentions that the workflow is trying to run a version of pip that does not exist inside the container.
The container image ghcr.io/iterative/cml:0-dvc3-base1 comes with Python 3.8.10 pre-installed. There is no Python 3.13 in this image, regardless of whether you use actions/setup-python in your workflow. This is because:

• When you specify a container: in your workflow, all steps run inside that container, and the container’s environment (including its installed Python version) is fixed at build time.
• The actions/setup-python action does not work inside arbitrary containers. It is only effective on standard GitHub-hosted runners, where it installs Python into a directory on the runner’s host OS.
• If you use container:, even on a self-hosted runner, the job runs inside the specified Docker container, which is isolated from the host. Any attempt by actions/setup-python to change the Python version will affect the host, not the running container.
• As a result, you cannot use actions/setup-python to install or change the Python version inside a container. If you need a different Python version (such as 3.13), you must use a container image that already includes it, or build your own custom image with the desired Python version pre-installed.

[tomhaber]

I'm trying to use a different version of Python together with cml without building my own images. I did some investigating myself and found that python (and pip) are installed inside of the container by setup-python but the paths are incorrect

pip contains a shebang pointing to the incorrect python location: /data/actions-runners/github-static-runner-1/_work/_tool/Python/3.12.10/x64/bin/python

[mahabaleshwars]

Hi @tomhaber,
To resolve this, please try clearing the Python cache:

- name: Clear Python cache
  run: |
        sudo rm -rf /__t/Python

Additionally, I would recommend using actions/cache for more reliable and configurable caching—especially when working with containers.
For reference, you can also check the advanced usage guide for setup-python with a self-hosted runner.

Let me know if you have any questions or need further assistance!

[tomhaber]

Did anything change? My conclusion was that the current setup can never work in the container and I worked around this issue accordingly