"""
---------------------------------------------------------------------
Verify that after() silently does nothing if subject window closed.
The after( event never fres again after popup is closed, and no
error (exception) message is generated in the console window.

This may matter in Run Code's output poller if the output window is
closed but EOF is never posted by the reader thread (though that 
still should happen on kills).  It shoudn't matter for the auto-save
timer, because that is bound to the main Tk root of the application.
---------------------------------------------------------------------
"""

from tkinter import *

count = 0

def poll():
    global count
    print(count)
    count += 1
    popup.after(2000, poll)

root=Tk()
Label(root, text='root').pack()
popup = Toplevel(root)
Button(popup, text='poll',  command=poll).pack(fill=X)
Button(popup, text='close', command=popup.destroy).pack(fill=X)
root.mainloop()