Question

I have a signal handler to handle ctrl-c interrupt. If in the signal handler I want to read a variable set in my main script, is there an alternative to using a “global” statement when setting the variable?

I don’t mind doing this, but read this post (Do you use the "global" statement in Python?) in which someone commented that there should be no reason to ever use global.

What is the alternative in this case?

My code looks like this:

def signal_handler(signal, frame):
    print "in sig handler - g_var=%s" % g_var

def main():
    global g_var
    g_var = "test"

    time.sleep(120)


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

Answer 1

You can use a closure as the signal handler that acquires its state from the main script:

import signal
import sys
import time

def main_function():

    data_for_signal_handler = 10

    def signal_handler(*args):
        print data_for_signal_handler
        sys.exit()

    signal.signal(signal.SIGINT, signal_handler) # Or whatever signal

    while True:
        data_for_signal_handler += 1
        time.sleep(0.5)

if __name__ == '__main__':
    main_function()