Saving work after a SIGINT

Question

I have a program which takes a long time to complete. I would like it to be able to catch SIGINT (ctrl-c) and call the self.save_work() method.

As it stands, my signal_hander() does not work since self is not defined by the time the program reaches signal_handler().

How can I set it up so self.save_work gets called after a SIGINT?

#!/usr/bin/env python
import signal 

def signal_handler(signal, frame):    
    self.save_work()   # Does not work
    exit(1)
signal.signal(signal.SIGINT, signal_handler)

class Main(object):
    def do_stuff(self):
        ...
    def save_work(self):
        ...
    def __init__(self):
        self.do_stuff()
        self.save_work()

if __name__=='__main__':
    Main()

Answer 1

Usually, "work" involves some kind of a big loop. To tame your loop, and prevent it from breaking in an unknown step, you can use the following context manager:

import signal

class GracefulInterruptHandler(object):

    def __init__(self, sig=signal.SIGINT):
        self.sig = sig

    def __enter__(self):

        self.interrupted = False
        self.released = False

        self.original_handler = signal.getsignal(self.sig)

        def handler(signum, frame):
            self.release()
            self.interrupted = True

        signal.signal(self.sig, handler)

        return self

    def __exit__(self, type, value, tb):
        self.release()

    def release(self):

        if self.released:
            return False

        signal.signal(self.sig, self.original_handler)

        self.released = True

        return True

To use:

import time

/// do stuff:
with GracefulInterruptHandler() as h:
    for i in xrange(1000):
        print "..."
        time.sleep(1)
        if h.interrupted:
            print "interrupted!"
            time.sleep(5)
            break

save_work()

From here: https://gist.github.com/2907502

Answer 2

import signal

def signal_handler(signal, frame):    
   #do some stuff

def main():
   #do some more stuff


if __name__=='__main__':
    signal.signal(signal.SIGINT, signal_handler)
    main()

Answer 3

If you just want to catch ctr+c then you can catch the KeyboardInterrupt exception:

class Main(object):
    def do_stuff(self):
        ...
    def save_work(self):
        ...
    def __init__(self):
        try:
            self.do_stuff()
        except KeyboardInterrupt:
            pass # Or print helpful info
        self.save_work()

Not that I think this is a good design after all. It looks like you need to be using a function instead of a constructor.