Run pip outside of environment

At a glance:

$ virtualenv --no-pip myenv  # Create environment without pip.

$ source myenv/bin/activate  # Activate environment.

$ pip --version      # pip is not available.
bash: pip: command not found

$ ouo install six    # But we can still do this.
Collecting six
  Using cached six-1.15.0-py2.py3-none-any.whl (10 kB)
Installing collected packages: six
Successfully installed six-1.15.0

$ python -c 'import six; print(six.__file__)'
.../myenv/lib/python3.9/site-packages/six.py

How?

ouo downloads pip wheels into the user's data dirctory. When executed, it executes pip with something like

/path/to/python /path/to/pip-20.3.3-py2.py3-none-any.whl/pip

where the path of the Python interpreter is detected with the VIRTUAL_ENV environment variable. The interpreter would then perform a zip import to execute the pip module inside the wheel.

Future Works

• setuptools and wheel are still needed to build legacy (non-PEP-517) source distributions. This makes python -m venv --no-pip unrealistic.
• Invocation is slow. This has two causes: ouo needs to iterate through the wheel directory to find a suitable pip version for the current Python version. Also, zip imports are very slow.