Python subprocess.call issue

Question

When I run the following in Python 3.2.3 in Linux it does nothing...

subprocess.call("export TZ=Australia/Adelaide", shell=True)

However if I run it in the terminal it works...

export TZ=Australia/Adelaide

I haven't had an issue with using subprocess.call before. Just seems to be this one. I'm running as a superuser so it's not a sudo thing, and I've also tried putting an r in front of the string to make it a raw string.

Any ideas? Thanks.

• metatoaster: If you want to modify environment variables within Python read up on os.environ.
• Cameron: @metatoaster I've got this but it is still only a local scope within the program. When I exit the program it remains as it was. Is there a way to make the OS update permanently? os.environ['TZ'] = 'Australia/Adelaide' time.tzset()
• metatoaster: You need to invoke OS/shell specific method of modifying this, such as modifying .bashrc, /etc/environment, or /etc/timezone if your Linux distribution supports that.
• jfs: related: Calling the "source" command from subprocess.Popen

Answer 1

Export modifies the environment of the shell.

When you run it through subprocess, a new shell is created, the environment modified and then immediately destroyed.

When you run it in a shell, it modifies the environment of that shell so you can see the effect.

Answer 2

A subprocess (shell in this case) can't (normally) modify its parent environment.

To set the local timezone for the script and its children in Python (on Unix):

#!/usr/bin/env python3
import os
import time
from datetime import datetime, timezone
os.environ['TZ'] = 'Australia/Adelaide'
time.tzset()
print(datetime.now(timezone.utc).astimezone())
# -> 2015年09月25日 05:02:52.784404+09:30

If you want to modify the environment for a single command then you could pass env parameter:

#!/usr/bin/env python
import os
import subprocess
subprocess.check_call('date', env=dict(os.environ, TZ='Australia/Adelaide'))
# -> Fri Sep 25 05:02:34 ACST 2015