I have created a virtualenv using the --no-site-packages option and installed lots of libraries. Now I would like to revert the --no-site-packages option and use also the global packages.

Can I do that without recreating the virtualenv?

More precisely:

I wonder what exactly happens when creating a virtualenv using the --no-site-packages option as opposed to not using that option.

If I know what happens then I can figure out how to undo it.

Try removing (or renaming) the file no-global-site-packages.txt in your Lib folder under your virtual environment.

Where venv is the name of your virtual environment, and python3.4 corresponds to whichever version of python involved, for example:

$ rm venv/lib/python3.4/no-global-site-packages.txt

And if you change your mind and want to put it back:

$ touch venv/lib/python3.4/no-global-site-packages.txt

Note: If you don’t see the above file, then you have a newer version of virtualenv. You’ll want to follow this answer instead

At least for Python 3.5.2, there is pyvenv.cfg file in the root of virtualenv directory. All you need to do is to change include-system-site-packages flag from false to true:

home = /usr/bin
include-system-site-packages = false  # <- change this to "true"
version = 3.5.2

When using virtualenvwrapper to manage virtualenvs, you can use the shell function toggleglobalsitepackages to switch between using and not using site packages.

Try adding a symlink between /virtualenv_root/lib/ and /path/to/desired/site-packages/

Go to your venv folder and open pyvenv.cfg. (E.g. if your virtual environment is called myenv then the file will be located at myenv\pyvenv.cfg)

You’ll see a boolean setting called include-system-site-packages

Set that setting to true to use global packages

If you want to disable using global packages, just set that setting to false instead.