Button Interrupts 

Hardware

Python

#!/usr/bin/env python2.7
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)

# GPIO 23 set up as input. It is pulled up to stop false signals
GPIO.setup(23, GPIO.IN, pull_up_down=GPIO.PUD_UP)

print "Make sure you have a button connected so that when pressed"
print "it will connect GPIO port 23 (pin 16) to GND (pin 6)\n"
raw_input("Press Enter when ready\n>")

print "Waiting for falling edge on port 23"
# now the program will do nothing until the signal on port 23 
# starts to fall towards zero. This is why we used the pullup
# to keep the signal high and prevent a false interrupt

print "During this waiting time, your computer is not" 
print "wasting resources by polling for a button press.\n"
print "Press your button when ready to initiate a falling edge interrupt."
try:
    GPIO.wait_for_edge(23, GPIO.FALLING)
    print "\nFalling edge detected. Now your program can continue with"
    print "whatever was waiting for a button press."
except KeyboardInterrupt:
    GPIO.cleanup()       # clean up GPIO on CTRL+C exit
GPIO.cleanup()           # clean up GPIO on normal exit

Test and Result

#!/usr/bin/env python
from time import sleep
import os 
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
GPIO.setup(23, GPIO.IN)

while True:
if ( GPIO.input(23) == False ):
print("Printing")
os.system("fortune -s science | python printer_device.py")
print("Printed")


sleep(1)

import printer, textwrap, sys 

p=printer.ThermalPrinter(serialport="/dev/ttyAMA0") 
unwrapped_text = sys.stdin.read() 
wrapped_text = textwrap.fill(unwrapped_text, 32) 
p.print_text(wrapped_text)
p.linefeed() 
p.linefeed() 
p.linefeed()
Modify the /etc/rc.local file to run this program anytime.
sudo nano /etc/rc.local 

Add this before exit0 :
cd /home/pi/printer/ && python gpio_test.py &

Reference

1. http://raspi.tv/2013/how-to-use-interrupts-with-python-on-the-raspberry-pi-and-rpi-gpio
2. http://geekgurldiaries.blogspot.hk/2012_12_01_archive.html