How to immediately kill and restart a thread while using a time.sleep() inside it?

[philipbergwerf]

I made this little example where a cursor is blinking on the canvas:

from tkinter import *
from threading import Thread
from time import sleep
 
root = Tk()
 
canvas = Canvas(root)
canvas.pack()

cursor_blink = True

def cursor():
    while cursor_blink:
        canvas.create_line(100,100,100,200,tag='cursor')
        sleep(0.5)
        canvas.delete('cursor')
        sleep(0.5)

thread = Thread(target=cursor)
thread.start()

def reset_cursor(evt):
    # kill cursor thread? / this function is supposed to restart the thread; how?
    thread.start()

root.bind('<ButtonRelease-1>', reset_cursor)
 
root.mainloop()

The goal is to reset the cursor immediately when clicking on the canvas. Currently it waits for the loop to complete before checking if the curs variable is still True. Is there maybe a different way without using sleep() to make the cursor blink?

[Jeff_t]

Instead of blocking the thread with sleep use time as a condition

import time

start=time.time()
end=0
elapsed=0
x=0

while True:

	if 0.0 <=elapsed <=0.5:
		print("On")
	elif 0.5 <=elapsed <=1:
		print("Off")
	elif elapsed >1:
		start=time.time()
		x+=1

	end=time.time()
	elapsed=end-start

	if x>=10:
		break

[Gribouillis]

I wrote a blinker using the tkinter after() method, without threads. Normally, threads other than the main thread should not update the state of the GUI

from tkinter import *
  
root = Tk()
  
canvas = Canvas(root)
canvas.pack()

class Blinker:
    def __init__(self, canvas, tag):
        self.canvas = canvas
        self.tag = tag
        self.delay = 500
        self.job = None
        
    def _negate(self, state):
        return 'hidden' if state == 'normal' else 'normal'
        
    def start(self, state='normal'):
        if self.job is not None:
            self.canvas.after_cancel(self.job)
            self.job = None
        self.canvas.itemconfigure(self.tag, state=state)
        self.job = self.canvas.after(self.delay, self.toggle)
        
    def toggle(self):
        state = self.canvas.itemcget(self.tag, 'state')
        self.canvas.itemconfigure(self.tag, state=self._negate(state))
        self.job = self.canvas.after(self.delay, self.toggle)
        
    def stop(self, state=None):
        if self.job is not None:
            self.canvas.after_cancel(self.job)
            self.job = None
        if state is not None:
            self.canvas.itemconfigure(self.tag, state=state)

    def reset(self, event):
        self.start()

canvas.create_line(100,100,100,200,tag='cursor')
blinker = Blinker(canvas, 'cursor')
blinker.start()
 
root.bind('<ButtonRelease-1>', blinker.reset)
  
root.mainloop()

[philipbergwerf]

Normally, threads other than the main thread should not update the state of the GUI

Why is that? why should I not do that?

[Gribouillis]

Actually, I'm probably wrong in this belief. However, read the paragraph about the threading model in the Tkinter documentation.