How to break out of a while True: loop with a button

Question

I've been working on some python scripts accessing the gpio pins on my rpi to light an led and I ran into a little problem I'm not sure how to solve.

My code looks something like this minus some setup statements

def ledblink():

while True:

GPIO.output(13, True)

time.sleep(.5)

GPIO.output(13, False)

time.sleep(.5)

def ledoff():

GPIO.output(13, False)

button = Button(root, text = 'LED ON', command = ledblink)

button.pack()

offbutton = Button(root, text = 'LED OFF', command = ledoff)

offbutton.pack()

As you can probably tell using tkinter for my gui. Also, as you can probably tell once I click the on button, that is all this program is going to let me do, the led blinks and continues because True is always True. How can I keep an indefinite loop running so that I can have a blinking led and still be able to break out of the loop when I want to turn things off? This was easy when I wanted to simply turn the led on and off, but not so easy with the loop I have to make it blink.

Just an FYI I was able to break out of the loop in my script version by using a try/except in which I used KeyboardInterrupt to call GPIO.cleanup() but I'm not sure how to do this in a gui.

e14 Contributor · Accepted Answer

Here's an entire working code that you can save and run, I have used a thread for ease of use and responsiveness as well as system efficiency. There are really only 4 extra lines of code to produce the threaded alternative, I also added a few extra bits here and there. Making global variables writeable within functions for simplicity. Any questions please just ask! I'm here to help rather than say what you should/shouldn't be doing, I'll always respond by providing tested functioning code import Tkinter as tk 
import time
import threading

switch = True
root = tk.Tk()

def blink():
 def run():
 while (switch == True):
 print('BLINK...BLINK...')
 time.sleep(0.5)
 if switch == False:
 break
 thread = threading.Thread(target=run)
 thread.start()

def switchon(): 
 global switch
 switch = True
 print 'switch on' 
 blink() 
 
def switchoff(): 
 print 'switch off'
 global switch
 switch = False 
 
def kill(): 
 root.destroy() 
 
onbutton = tk.Button(root, text = "Blink ON", command = switchon) 
onbutton.pack() 
offbutton = tk.Button(root, text = "Blink OFF", command = switchoff) 
offbutton.pack() 
killbutton = tk.Button(root, text = "EXIT", command = kill) 
killbutton.pack() 
 
root.mainloop()

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