Python advice using delays with tkinter

Question

I have created GUI using tkinter, which will run on the RaspberryPi and will perform various actions such as lighting LEDs. The problem I have is toggling an LED on and off using the root.after scheduling as if I use time.sleep(), the GUI will freeze while in this sleep. Here is my code, below I want to replace time.sleep() with some kind of delay roughly 500ms.

def toggleLED(root,period=0):
    if (period <15) and (Status is "On"):
            GPIO.output(11, True)
            time.sleep(0.5) #Needs to be replaced as causing GUI to freeze
            GPIO.output(11, False)
            root.after(1000, lambda: toggleLED(root, period)) #schedule task every 1 second while condition is true
    elif (Status == "Off"):
            print("Lights have been switched off")
    else:
            GPIO.output(11, True)

thanks

This is one solution, but it seems very messy:

def toggleLED(root,period=0):
    global Flash
    while (period <30) and (Status is "On"):
            if (Flash is True):
                    GPIO.output(11, False)
                    Flash = False
                    break
            elif (Flash is False):
                    GPIO.output(11, True)
                    Flash = True
                    break
            else:
                    break
    if (period <30) and (Status == "On"):
            period +=1
            print(period)
            root.after(500, lambda: toggleLED(root, period))
    elif (Status == "Off"):
           print("Lights have been switched off")
    else:
           GPIO.output(11, True)

Your solution can be cleaned by removing duplicate code and unnecessary blocks. However, what is the result you want to achieve? Toggling the light 30 times? — A. Rodas
– A. Rodas, Commented Mar 25, 2013 at 16:47
Yes the light should toggle 30 times within a 15 second period. — user2207573
– user2207573, Commented Mar 25, 2013 at 18:57

Bryan Oakley · Accepted Answer · 2013-05-18 22:09:16Z

Part of the problem is your while loop -- you don't need any sort of loop since you have the event loop.

Here's an example of toggling a label every 500ms for 30 seconds:

import Tkinter as tk

class Example(tk.Frame):

    def __init__(self, *args, **kwargs):
        tk.Frame.__init__(self, *args, **kwargs)
        self._job_id = None

        self.led = tk.Label(self, width=1, borderwidth=2, relief="groove")
        self.start_button = tk.Button(self, text="start", command=self.start)
        self.stop_button = tk.Button(self, text="stop", command=self.stop)

        self.start_button.pack(side="top")
        self.stop_button.pack(side="top")
        self.led.pack(side="top")

    def stop(self):
        if self._job_id is not None:
            self.after_cancel(self._job_id)
            self._job_id = None
            self.led.configure(background="#ffffff")

    def start(self):
        self._job_id = self.after(500, lambda: self.toggle(60))

    def toggle(self, counter):
        bg = self.led.cget("background")
        bg = "#ffffff" if bg == "#ff0000" else "#ff0000"
        self.led.configure(background=bg)
        if counter > 1:
            self._job_id = self.after(500, lambda: self.toggle(counter-1))

root = tk.Tk()
Example(root).pack(side="top", fill="both", expand=True)
root.mainloop()

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