Python Virtual Environment should respect ${VIRTUAL_ENV}

[theelderbeever]

In this section of code you can provide directories with which to look for virtual environments. There should be a way to respect the ${VIRTUAL_ENV} environment variable for active environments. ie: Just use the absolute path in that variable if it is set. A lot of people use pyenv or other solutions which leverage this variable. Simply doing source ${VIRTUAL_ENV}/bin/activate feels like it would solve a lot of problems with picking environments.

Additionally why not provide a fully custom activate_script input instead of enforcing shells. That way I (the user) could just set my activate script to pyenv activate my-venv?

Per the docs.python.org

When a virtual environment has been activated, the VIRTUAL_ENV environment variable is set to the path of the environment.

#7808 for reference