How to stop SIGINT being passed to subprocess in python?

Signal handlers are inherited when you start a subprocess, so if you use the signal module to ignore SIGINT (signal.signal(signal.SIGINT, signal.SIG_IGN)), then your child process automatically will also.

There are two important caveats, though:

• You have to set the ignore handler before you spawn the child process
• Custom signal handlers are reset to the default handlers, since the child process won't have access to the handler code to run it.

So if you need to customise your handling of SIGINT rather than just ignoring it, you probably want to temporarily ignore SIGINT while you spawn your child process, then (re)set your custom signal handler.

If you're trying to catch SIGINT and set a flag so you can exit at a safe point rather than immediately, remember that when you get to that safe point your code will have to manually clean up its descendants, since your child process and any processes it starts will be ignoring the SIGINT.

You are able to re-assign the role of ctrl-c using the tty module, which allows you to manipulate the assignment of signals. Be warned, however, that unless you put them back the way they were before you modified them, they will persist for the shell's entire session, even after the program exits.

Here is a simple code snippet to get you started that stores your old tty settings, re-assigns ctrl-c to ctrl-x, and then restores your previous tty settings upon exit.

import sysimport tty# Back up previous tty settingsstdin_fileno = sys.stdin.fileno()old_ttyattr = tty.tcgetattr(stdin_fileno)try:    print 'Reassigning ctrl-c to ctrl-x'    # Enter raw mode on local tty    tty.setraw(stdin_fileno)    raw_ta = tty.tcgetattr(stdin_fileno)    raw_ta[tty.LFLAG] |= tty.ISIG    raw_ta[tty.OFLAG] |= tty.OPOST | tty.ONLCR    # ^X is the new ^C, set this to 0 to disable it entirely    raw_ta[tty.CC][tty.VINTR] = '\x18'      # Set raw tty as active tty    tty.tcsetattr(stdin_fileno, tty.TCSANOW, raw_ta)    # Dummy program loop    import time    for _ in range(5):        print 'doing stuff'        time.sleep(1)finally:    print 'Resetting ctrl-c'    # Restore previous tty no matter what    tty.tcsetattr(stdin_fileno, tty.TCSANOW, old_ttyattr)

For python 2 codebase: subprocess is broken.

The right thing is

import subprocess32 as subprocess

See subprocess32

This is a backport of the Python 3 subprocess module for use on Python2. This code has not been tested on Windows or other non-POSIX platforms.