How to detect if python script is being run as a background process

Question

Is there a way to tell whether my python script is running as a background process or not? I'm trying to differentiate between these two:

sudo ./myscript.py
sudo ./myscript.py &

Using sys.argv doesn't work - the ampersand doesn't count as an argument apparently. And what would be the effect of the following instead:

sudo python myscript.py
sudo python myscript.py &

I've had a look around, but everything seems to be about starting a background process from within a Python script, not whether the Python script itself is a background process. Thanks!

EDIT: The aim is to output a message (or not), i.e. "Press Ctrl+C to stop this script" if started normally, but don't display the message if started as a background process.

EDIT 2 I neglected to mention that this python script will be started by a script in /etc/init.d rather than from a terminal prompt. So the answer marked as correct does indeed answer the question as I phrased it and with the information given, but I thought I should point out that it doesn't work in the init.d scenario, to avoid any potential confusion in the future.

Answer 1

Based on the answer for C @AaronDigulla pointed to in a comment:

import os
import sys


def main():
    if os.getpgrp() == os.tcgetpgrp(sys.stdout.fileno()):
        print 'Running in foreground.'
    else:
        print 'Running in background.'


if __name__ == '__main__':
    main()

Answer 2

I saw the other solutions on other and decided to write a pure python solution. It reads from /proc/<pid>/stat rather than calling a subprocess.

from os import getpid

with open("/proc/{}/stat".format(getpid())) as f:
    data = f.read()

foreground_pid_of_group = data.rsplit(" ", 45)[1]
is_in_foreground = str(getpid()) == foreground_pid_of_group

The meanings of the columns of the stat file can be found here

Answer 3

Based on bash solution from this answer:

import os
import subprocess
pid = os.getpid()
if "+" in subprocess.check_output(["ps", "-o", "stat=", "-p", str(pid)]):
  print "Running in foreground"
else:
  print "Running in background"