How to deal with environment variables using python script

Any OS like Linux, Unix, Windows has environment variables.
Also any variables which must not be committed on a public code can be used in this way.
You can give this variables to your application.
Let's see one simple example about how to do that:

import os
ENV_VAR = os.environ.get("ENV_VAR", None)
if not ENV_VAR:
        print "not ENV_VAR"
if ENV_VAR:
        print "yes ! is ENV_VAR"

Now you can give this ENV_VAR to the script or not. See next...

usertest@home:~$ ENV_VAR=true python demo-env.py 
yes ! is ENV_VAR
usertest@home:~$ python demo-env.py 
not ENV_VAR

With Python 3 on Unix, environment variables are decoded using the file system encoding.