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.)
This question is related to
python
environment-variables
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/'
Use os.environ[str(DEBUSSY)]
for both reading and writing (http://docs.python.org/library/os.html#os.environ).
As for reading, you have to parse the number from the string yourself of course.
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.
If you want to pass global variables into new scripts, you can create a python file that is only meant for holding global variables (e.g. globals.py). When you import this file at the top of the child script, it should have access to all of those variables.
If you are writing to these variables, then that is a different story. That involves concurrency and locking the variables, which I'm not going to get into unless you want.
Source: Stackoverflow.com