Python: How to prevent subprocesses from receiving CTRL-C / Control-C / SIGINT

Combining some of other answers that will do the trick - no signal sent to main app will be forwarded to the subprocess.

import os
from subprocess import Popen

def preexec(): # Don't forward signals.
    os.setpgrp()

Popen('whatever', preexec_fn = preexec)

you can do something like this to make it work in windows and unix:

import subprocess
import sys

def pre_exec():
    # To ignore CTRL+C signal in the new process
    signal.signal(signal.SIGINT, signal.SIG_IGN)

if sys.platform.startswith('win'):
    #https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863(v=vs.85).aspx
    #CREATE_NEW_PROCESS_GROUP=0x00000200 -> If this flag is specified, CTRL+C signals will be disabled
    my_sub_process=subprocess.Popen(["executable"], creationflags=0x00000200)
else:
    my_sub_process=subprocess.Popen(["executable"], preexec_fn = pre_exec)

Somebody in the #python IRC-Channel (Freenode) helped me by pointing out the preexec_fn parameter of subprocess.Popen(...):

If preexec_fn is set to a callable object, this object will be called in the child process just before the child is executed. (Unix only)

Thus, the following code solves the problem (UNIX only):

import subprocess
import signal

def preexec_function():
    # Ignore the SIGINT signal by setting the handler to the standard
    # signal handler SIG_IGN.
    signal.signal(signal.SIGINT, signal.SIG_IGN)

my_process = subprocess.Popen(
    ["my_executable"],
    preexec_fn = preexec_function
)

Note: The signal is actually not prevented from reaching the subprocess. Instead, the preexec_fn above overwrites the signal's default handler so that the signal is ignored. Thus, this solution may not work if the subprocess overwrites the SIGINT handler again.

Another note: This solution works for all sorts of subprocesses, i.e. it is not restricted to subprocesses written in Python, too. For example the dedicated server I am writing my wrapper for is in fact written in Java.