I think I would do that instead:

```
.build-artefacts/translate-requirements-installation.timestamp: .build-artefacts/python-venv
    .build-artefacts/python-venv/bin/pip install "psycopg2==2.5.1"
    .build-artefacts/python-venv/bin/pip install "PyYAML==3.10"
    touch $@
```