Prevent tox from reinstalling dependencies that are pre-installed in a Docker image

[omerkarpas]

I'm running tox inside a Docker container where all dependencies are pre-installed. However, even when setting sitepackages = true, tox still attempts to install packages instead of using the system-wide ones.

My Dockerfile (Dependency Installation)

COPY image-requirements.txt .
RUN pip install --no-cache-dir -r image-requirements.txt --user

# Install Playwright browsers
RUN playwright install chromium

• Tried with and without --user**,

My tox.ini Configuration

[tox]
envlist = ci

[testenv:ci]
sitepackages = true
usedevelop = true
install_command = pip install --exists-action=w -r requirements.txt
commands =
    pytest {posargs}
passenv = *

Issue:

Even though sitepackages = true, tox still tries to install dependencies. My goal is for tox to reuse the already installed packages instead of reinstalling them.

Expected Behavior:

• tox should use the existing dependencies without reinstalling them, if it finds it in system level. if it dosent, it should install.

Questions:

1. How can I force tox to only use system-installed dependencies instead of installing them?
2. Does sitepackages = true not work when dependencies are installed with --user?
3. Would using a different install_command or modifying PYTHONPATH work?

Thanks in advance for any help! 🚀

[gaborbernat]

This is not supported and out of scope for this project. You can try to create a plugin to achieve this, however, I'm not entirely sure how you would achieve this, even with a plugin.

[omerkarpas]

so please explain what is sitepackages = true for?

[gaborbernat]

Give the virtual environment access to the system site-packages dir. Means you have access to that, however if you try installing again that's a pip behaviour that will try to reinstall it.

[omerkarpas]

By ditching Tox, and just using - "pip install -e ." i was able to achieve what i wanted.