How to perform os.environ join in python?

Question

I have a configuration of os.environ with default values (that cover 90% of my needs). I have a special application-framework-package, for example called SALOME, that does not provide package installation into system environment and tries to be self contained, it also requires use of special old technologies that rely on environmental variables thus sys.path and PYTHONPATH are not the only things it needs. I can get all variables it needs when it started calling os.environ inside an environment it creates. I can then serialize that os.environ dictionary.

I wonder how to apply a merge of os.environ I have on my currently running system with one I obtained by serializing?

Answer 1

Let's assume you have done something like the following to serialize the environment:

import json
import os

with open('environ.json', 'w') as f:
    json.dump(dict(**os.environ), f)

You can now read those back like this (in another program)

import json
import os

with open('environ.json', 'r') as f:
    os.environ.update(json.load(f))

This will only add or change the current environment variables to match the saved ones, but any additional variables will remain.

If you want to update only specific variables by adding them (so for instance to add extra paths), you can do that explicitly:

with open('environ.json', 'r') as f:
    loadedenv = json.load(f)

pathvars = ['PATH', 'PYTHONPATH']

for p in pathvars:
    os.environ[p] += ':' + loadedenv[p]