Terry J. Reedy added the comment:
IDLE uses tk/tkinter text widgets for Editor and Shell windows. A known
downside of this is that long lines, greater than about 2000 chars, slow down
scrolling. See #1442493 for instance.
Part of the Squeezer feature was meant to alleviate this by
New submission from A A :
Idle3 with python 3.7.3 on Debian Buster and XFCE.
Attempting to run the line 'print ("Hello World" * 8**8)' from either the Idle
shell window or Idle editor will cause Idle to hang and one CPU core runs
100%.(allowed it to run for several minutes)
ctl+c or menu
