Reading and writing environment variables in Python? [duplicate]

My python script which calls many python functions and shell scripts. I want to set a environment variable in Python (main calling function) and all the daughter processes including the shell scripts to see the environmental variable set.

I need to set some environmental variables like this:

DEBUSSY 1
FSDB 1

1 is a number, not a string. Additionally, how can I read the value stored in an environment variable? (Like DEBUSSY/FSDB in another python child script.)

Solution 1:

Try using the os module.

import os

os.environ['DEBUSSY'] = '1'
os.environ['FSDB'] = '1'

# Open child processes via os.system(), popen() or fork() and execv()

someVariable = int(os.environ['DEBUSSY'])

See the Python docs on os.environ. Also, for spawning child processes, see Python's subprocess docs.

Solution 2:

First things first :) reading books is an excellent approach to problem solving; it's the difference between band-aid fixes and long-term investments in solving problems. Never miss an opportunity to learn. :D

You might choose to interpret the 1 as a number, but environment variables don't care. They just pass around strings:

   The argument envp is an array of character pointers to null-
   terminated strings. These strings shall constitute the
   environment for the new process image. The envp array is
   terminated by a null pointer.

(From environ(3posix).)

You access environment variables in python using the os.environ dictionary-like object:

>>> import os
>>> os.environ["HOME"]
'/home/sarnold'
>>> os.environ["PATH"]
'/home/sarnold/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games'
>>> os.environ["PATH"] = os.environ["PATH"] + ":/silly/"
>>> os.environ["PATH"]
'/home/sarnold/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/silly/'