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

flypadre

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.

 

 

 

Parents
  • Former Member
    0 Former Member

    Interesting discussion.

     

    Typically, I write a more simplified threaded procedure so that the straight-line code avoids embedded procedures (my preference or "style").  For whatever it is worth,

     

    # Changes to original code on 2016-10-21 15:21 USA CT
# Simplified blink() procedure for future enhancement
# Moved threading references to main code section
# Doubled sleep time (not significant)
# Renamed "switch" to "flag_blinking" (not significant)
# Introduced flag_exiting

import Tkinter as tk    
import time  
import threading  
  
flag_blinking = False 
flag_exiting = False 

root = tk.Tk()  
  
def blink():  
    global flag_blinking  
    global flag_exiting   
    while ( True ):
        if (flag_blinking == True):  
            print('BLINK...BLINK...') 
        if (flag_exiting == True):
            return 
        time.sleep(1.0)  

def switchon():    
    global flag_blinking  
    flag_blinking = True  
    print 'flag_blinking on'   
        
def switchoff():    
    global flag_blinking  
    flag_blinking = False      
    print 'flag_blinking off'  
        
def kill(): 
    global flag_exiting   
    flag_exiting = True
    root.destroy()    
        
thread = threading.Thread(target=blink)  
thread.start()  

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()

Reply
  • Former Member
    0 Former Member

    Interesting discussion.

     

    Typically, I write a more simplified threaded procedure so that the straight-line code avoids embedded procedures (my preference or "style").  For whatever it is worth,

     

    # Changes to original code on 2016-10-21 15:21 USA CT
# Simplified blink() procedure for future enhancement
# Moved threading references to main code section
# Doubled sleep time (not significant)
# Renamed "switch" to "flag_blinking" (not significant)
# Introduced flag_exiting

import Tkinter as tk    
import time  
import threading  
  
flag_blinking = False 
flag_exiting = False 

root = tk.Tk()  
  
def blink():  
    global flag_blinking  
    global flag_exiting   
    while ( True ):
        if (flag_blinking == True):  
            print('BLINK...BLINK...') 
        if (flag_exiting == True):
            return 
        time.sleep(1.0)  

def switchon():    
    global flag_blinking  
    flag_blinking = True  
    print 'flag_blinking on'   
        
def switchoff():    
    global flag_blinking  
    flag_blinking = False      
    print 'flag_blinking off'  
        
def kill(): 
    global flag_exiting   
    flag_exiting = True
    root.destroy()    
        
thread = threading.Thread(target=blink)  
thread.start()  

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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