Handling signals in Python inside a function

I have code that needs to exit gracefully. To simplify things, I am presenting an example based on the answer given here.

Since I need to handle a few signals, I thought of putting this logic in a function:

def set_signals():
   original_sigint = signal.getsignal(signal.SIGINT)
   signal.signal(signal.SIGINT, exit_gracefully)
   signal.signal(signal.SIGTERM, exit_gracefully)
   signal.signal(signal.SIGINT, exit_gracefully)
   signal.signal(signal.SIGALRM, exit_gracefully)
   signal.signal(signal.SIGHUP, signal.SIG_IGN)

Thus, the main block of the python code should be:

if __name__ == '__main__':
    # store the original SIGINT handler
    set_signals()
    run_program()

This will fail however, since the exit_gracefully does not know the variable original_init.

Therefore, my solution was to create original_sigint as a global variable.

```
import signal
import time
import sys

original_sigint = None

def run_program():
while True:
time.sleep(1)
print("a")

def exit_gracefully(signum, frame):
# restore the original signal handler as otherwise evil things will happen
# in raw_input when CTRL+C is pressed, and our signal handler is not re-entrant
global original_sigint
signal.signal(signal.SIGINT, original_sigint)

try:
if raw_input("\nReally quit? (y/n)> ").lower().startswith('y'):
sys.exit(1)

except KeyboardInterrupt:
print("Ok ok, quitting")
sys.exit(1)

# restore the exit gracefully handler here
signal.signal(signal.SIGINT, exit_gracefully)

def set_signals():
global original_sigint
original_sigint = signal.getsignal(signal.SIGINT)
signal.signal(signal.SIGINT, exit_gracefully)
signal.signal(signal.SIGTERM, exit_gracefully)
signal.signal(signal.SIGINT, exit_gracefully)
signal.signal(signal.SIGALRM, exit_gracefully)
signal.signal(signal.SIGHUP, signal.SIG_IGN)

if __name__ == '__main__':
# store the original SIGINT hand

What about implementing your signal handling code inside a class? This could look something like the following:

class GracefulExit:
    def __enter__(self):
        # set up signals here
        # store old signal handlers as instance variables

    def __exit__(self, type, value, traceback):
        # restore old signal handlers

You can then use this in your code as follows:

with GracefulExit():
    # Signals will be caught inside this block.

# Signals will no more be caught here.

You'll find more examples of how to use the with-statement on the web.

StackExchange Code Review Q#54348, answer score: 8