Python virtualenv not activated or interpreter mismatch

Playbook ID: python-virtualenv-not-activated Category: build Severity: medium Tags: python, virtualenv, venv, interpreter, environment

What this failure means

Python code is using a system interpreter or wrong virtualenv instead of the activated one, causing module import failures or version mismatches.

Common log signals

activate: not found
source.*venv
/usr/bin/python.*No module named
venv/bin/activate
site-packages from system Python

Diagnosis

When a Python virtualenv is not activated or is deactivated mid-build, pip and modules are installed in the wrong location. Common causes:

• The virtualenv activation step (e.g., source venv/bin/activate) was skipped or failed silently
• The build runs multiple shell invocations without persisting the activation across steps
• The script uses #!/usr/bin/env python which may resolve to the system interpreter, not the virtualenv one
• GitHub Actions or other CI steps start with a fresh shell that needs re-activation

Symptoms include ModuleNotFoundError for packages that were installed, or import failures from the wrong Python version.

Fix steps

1. Create and activate the virtualenv explicitly in your CI build script:

   python3 -m venv venv
   source venv/bin/activate  # On Windows: venv\Scripts\activate
   pip install -r requirements.txt
   python -m pytest
   

2. If using GitHub Actions, use actions/setup-python to manage the virtualenv:

   - uses: actions/setup-python@v4
     with:
       python-version: '3.11'
      cache: 'pip'
   - run: pip install -r requirements.txt
   - run: python -m pytest
   

3. If running multiple steps, either source the activation in each step or use a single shell script:

   - run: |
       source venv/bin/activate
       pip install -r requirements.txt
       python -m pytest
   

4. Verify the correct Python interpreter is in use:

   which python3
   python3 --version
   

Validation

• which python3 shows the path inside the virtualenv, not the system Python.
• python3 -c "import sys; print(sys.prefix)" shows the virtualenv directory.
• pip list shows the packages from requirements.txt.
• Re-run the test or build command successfully.

Likely files to inspect

• requirements.txt
• setup.py
• pyproject.toml
• .github/workflows/*.yml
• .gitlab-ci.yml

Run Faultline

faultline analyze build.log
faultline explain python-virtualenv-not-activated
faultline workflow build.log --json --mode agent

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