turtle won't crawl

[Pedroski55]

EDIT: a workaround is: restart the shell each time, somehow the window killer remains in memory. Any way to reset this without restarting the shell??

When I installed Python in Win 10 for the gf, I saw she had examples of turtle. A nice clock, for example. I did not know about turtle.

So I am looking at it, here in tutorialspoint.com. Thought it might be fun to show some kids.

I import turtle in the Idle shell:

import turtle     
from turtle import *

But I immediately get an error from this simple example to draw a square (and other simple examples):

def myApp():        
    my_pen = turtle.Turtle()      
    for i in range(4):
       my_pen.forward(50)           
       my_pen.right(90)               
    turtle.done()

The error in Idle is:

>>> myApp()
Traceback (most recent call last):
File "<pyshell#34>", line 1, in <module>
myApp()
File "<pyshell#33>", line 2, in myApp
my_pen = turtle.Turtle()
File "/usr/lib/python3.6/turtle.py", line 3816, in __init__
visible=visible)
File "/usr/lib/python3.6/turtle.py", line 2557, in __init__
self._update()
File "/usr/lib/python3.6/turtle.py", line 2660, in _update
self._update_data()
File "/usr/lib/python3.6/turtle.py", line 2646, in _update_data
self.screen._incrementudc()
File "/usr/lib/python3.6/turtle.py", line 1292, in _incrementudc
raise Terminator
turtle.Terminator

Does anyone know what is wrong?