How do I capture SIGINT in Python?

Question

I\'m working on a python script that starts several processes and database connections. Every now and then I want to kill the script with a Ctrl+C sign

Answer 1

You can handle CTRL+C by catching the KeyboardInterrupt exception. You can implement any clean-up code in the exception handler.

Answer 2

From Python's documentation:

import signal
import time

def handler(signum, frame):
    print 'Here you go'

signal.signal(signal.SIGINT, handler)

time.sleep(10) # Press Ctrl+c here

Answer 3

And as a 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:

with GracefulInterruptHandler() as h:
    for i in xrange(1000):
        print "..."
        time.sleep(1)
        if h.interrupted:
            print "interrupted!"
            time.sleep(2)
            break

Nested handlers:

with GracefulInterruptHandler() as h1:
    while True:
        print "(1)..."
        time.sleep(1)
        with GracefulInterruptHandler() as h2:
            while True:
                print "\t(2)..."
                time.sleep(1)
                if h2.interrupted:
                    print "\t(2) interrupted!"
                    time.sleep(2)
                    break
        if h1.interrupted:
            print "(1) interrupted!"
            time.sleep(2)
            break

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

Answer 4

Yet Another Snippet

Referred main as the main function and exit_gracefully as the CTRL + c handler

if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        pass
    finally:
        exit_gracefully()

Answer 5

I adapted the code from @udi to support multiple signals (nothing fancy) :

class GracefulInterruptHandler(object):
    def __init__(self, signals=(signal.SIGINT, signal.SIGTERM)):
        self.signals = signals
        self.original_handlers = {}

    def __enter__(self):
        self.interrupted = False
        self.released = False

        for sig in self.signals:
            self.original_handlers[sig] = signal.getsignal(sig)
            signal.signal(sig, self.handler)

        return self

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

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

    def release(self):
        if self.released:
            return False

        for sig in self.signals:
            signal.signal(sig, self.original_handlers[sig])

        self.released = True
        return True

This code support the keyboard interrupt call (SIGINT) and the SIGTERM (kill <process>)

Answer 6

Personally, I couldn't use try/except KeyboardInterrupt because I was using standard socket (IPC) mode which is blocking. So the SIGINT was cueued, but came only after receiving data on the socket.

Setting a signal handler behaves the same.

On the other hand, this only works for an actual terminal. Other starting environments might not accept Ctrl+C, or pre-handle the signal.

Also, there are "Exceptions" and "BaseExceptions" in Python, which differ in the sense that interpreter needs to exit cleanly itself, so some exceptions have a higher priority than others (Exceptions is derived from BaseException)