This is probably related to earlier problems with running IDLE on MacOS Catalina:

Environment:

MacOS Catalina:  10.15.5
Python: 3.7.3
IDLE: 3.7.3

Steps to reproduce:

- Open IDLE, create a new file.  (Can reopen this file again for subsequent tests.)

- Code can consist of a single line:

dontCare = input('While this prompt for input is up, press Command q: ')

- Save and run

- When you see the prompt, press Command q to quit.

- See correct dialog box:  Your program is still running!  Do you want to kill it?

- Press OK.

Results:

- Python program quits.  Source file window closes. IDLE is left in an "unstable" state with only the IDLE menu option available.

At this point, any attempt to do anything with IDLE crashes IDLE, and shows a Mac system dialog box:

IDLE quit unexpectedly.  Click Reopen to open the application. Click Report to .....


Note:  This is not a huge deal because I have to restart IDLE anyway because of a bug 38946, which does not allow me to allow me to double click on a Python file if IDLE is already running.  But I thought this new information might help track things down.



I have run in to this because I am correcting many student's homework files, where I ask them to build a loop where they ask the user for information, do some processing, and generate output with that information.  Then the loop goes around again and asks for input again.  I want to quit the application at that point, but I always end up crashing IDLE.