Question

How do I set, temporarily, the PYTHONPATH environment variable just before executing a Python script?

In *nix, I can do this:

$ PYTHONPATH='.' python scripts/doit.py

In Windows, this syntax does not work, of course. What is the equivalent, though?

Answer 1

To set and restore an environment variable on Windows’ command line requires an unfortunately “somewhat torturous” approach…:

SET SAVE=%PYTHONPATH%
SET PYTHONPATH=.
python scripts/doit.py
SET PYTHONPATH=%SAVE%

You could use a little auxiliary Python script to make it less painful, e.g.

import os
import sys
import subprocess

for i, a in enumerate(sys.argv[1:]):
    if '=' not in a: break
    name, _, value = a.partition('=')
    os.environ[name] = value

sys.exit(subprocess.call(sys.argv[i:]))

to be called as, e.g.,

python withenv.py PYTHONPATH=. python scripts/doit.py

(I’ve coded it so it works for any subprocess, not just a Python script — if you only care about Python scripts you could omit the second python in the cal and put ‘python’ in sys.argv[i-1] in the code, then use sys.argv[i-1:] as the argument for subprocess.call).