How to set environment variables in virtualenv

Question

If I have python script which activates the virtualenv like this:

#!/path/to/venv/bin/python

How can I set variables for this script without modifying this script?

I want this environment variable to be active for all scripts which use this virtualenv.

This means modifying this script is not a solution, since there are twenty scripts, and I don't want to modify twenty scripts.

Writing a shell wrapper-script around the python scripts would work, but I would like to avoid this.

In the past I thought a custom sitecustomize.py can be used for start-up code. But Ubuntu (AFAIK the only distribution which does this) comes with its own sitecustomize.py file, with the effect that my sitecustomize.py does not get called. See https://bugs.launchpad.net/ubuntu/+source/python2.5/+bug/197219

Here are some ways how I want to use the virtualenv:

• Script which gets executed via unix cron.
• virtualenv in a systemd service. See: How to enable a virtualenv in a systemd service unit?
• via mod_wsgi (Apache): https://modwsgi.readthedocs.io/en/develop/user-guides/virtual-environments.html#daemon-mode-single-application

(I have thought about this again. I guess it setting the variables is not the job of python or virtualenv. I need a unified way to set environment variables. And in my case I would like to do this without using a shell wrapper).

Answer 1

while writing sitecustomize.py file and changing bin/python all are feasible solutions, I would suggest another method that does not involve directly change contents inside virutalenv, by simply install a .pth file:

./venv/lib/python2.7/site-packages/_set_envs.pth

with content:

import os; os.environ['FOO'] = 'bar'

test:

$ ./venv/bin/python -c "import os; print os.getenv('FOO')"
bar

the trick is, python will load every .pth file on startup, and if there is a line starts with import, this line will be get executed, allowing inject arbitrary code.

the advantage is, you could simply write a python package to install this .pth file with setuptools, install to the virtualenv you want to change.

Answer 2

From what I have tried, it seems if you create a sitecustomize.py file inside the virtual environment, it will take precedence over the global sitecustomize.pyinstalled in /usr/lib/python2.7 directory. Here is what I did:

Create a sitecustomize.py in the virtual environment

$ echo "import os; os.environ['FOO'] = 'BAR'" > ~/venvs/env_test/lib/python2.7/sitecustomize.py

Verify that it is getting imported and executed when running the Python binary from the virtual environment

$ ~/venvs/env_test/bin/python
Python 2.7.15rc1 (default, Apr 15 2018, 21:51:34)
[GCC 7.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sitecustomize
>>> sitecustomize.__file__
'/home/abhinav/venvs/env_test/lib/python2.7/sitecustomize.py'
>>> import os
>>> os.environ['FOO']
'BAR'
>>>

Just to verify that FOO is set even without explicitly importing sitecustomize:

$ ~/venvs/env_test/bin/python
Python 2.7.15rc1 (default, Apr 15 2018, 21:51:34)
[GCC 7.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.environ['FOO']
'BAR'
>>>