GitHub Actions: Faster Python runs with cached virtual environments

github-actions-faster-python-virtual-environments.yml

# See https://adamj.eu/tech/2023/11/02/github-actions-faster-python-virtual-environments/
# ...

jobs:
  example:
    # ...

    steps:
      # ...

      - uses: actions/setup-python@v5
        id: setup-python
        with:
          python-version: '3.12'

      - uses: actions/cache/restore@v4
        id: cache-venv-restore
        with:
          key: venv-${{ runner.os }}-${{ steps.setup-python.outputs.python-version }}-${{ hashFiles('requirements.txt') }}
          path: .venv

      - name: Set up virtualenv
        run: |
          [[ ! -d .venv ]] && python -m venv .venv
          echo "VIRTUAL_ENV=${PWD}/.venv" >> ${GITHUB_ENV} && \
          echo "${PWD}/.venv/bin" >> ${GITHUB_PATH}

      - name: Install dependencies
        if: steps.cache-venv-restore.outputs.cache-hit != 'true'
        run: python -m pip install -r requirements.txt

      - uses: actions/cache/save@v4
        if: steps.cache-venv-restore.outputs.cache-hit != 'true'
        with:
          key: ${{ steps.cache-venv-restore.outputs.cache-primary-key }}
          path: .venv

      # ...