Including global package into a virtualenv that has been created with --no-site-packages

Question

I'd usually prefer to create virtualenvs with --no-site-packages option for more isolation, and also because default python global packages includes quite a lot of packages, and usually most of them are not needed. However I'd still want to keep a few select packages in global, like PIL or psycopg2. Is there a good way to include them into the virtualenv, that can also be automated easily?

Answer 1

If you're using virtualenvwrapper and you might be able to use the postmkvirtualenv script to automatically create symlinks in the new virtualenv sitepackages directory.

#!/bin/sh
cdsitepackages
ln -s /path/to/system/site-packages/package-name
cdvirtualenv

Answer 2

If you are using virtualenvwrapper, the shell command add2virtualenv should be present in an active virtualenv. Use:

add2virtualenv /path/to/package

to add an entry to the PTH file _virtualenv_path_extensions.pth in your virtualenv site-packages.

The benefit of using add2virtualenv rather than creating symlinks yourself, is that you can remove the package from being importable by commenting out its line in the PTH file. This makes it easier to check your code's validity against several versions of a library on which it depends.

Answer 3

I haven't actually tried this with those specific packages, but I would guess that a simple symlink from the global site-packages into the virtualenv's site-packages might work, and this is easily scriptable.