Maybe this will help to find a solution for your app:

import Tkinter as Tk

def stopPressed():
    # reset Poser events here
    app.cancel=True
    app.destroy()
    

app=Tk.Tk()
app.cancel=False
btn=Tk.Button(app,text="press to stop",command=stopPressed)
btn.pack()
app.update()

# Insert your standard app here.
# call app.update() from time to time and check
# app.cancel.

import math

for i in range(1000000) :
    # heavy work to do - the following makes no sense :)
    x=i*math.sin(i/100000.0)+math.acos(i/100000.0)
    app.update()
    if app.cancel : break
    
    for j in range(1000000) :
        y=x*math.cos(j/100000.0)

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