Thanks Ned and Terry for your responses.

Ned: I am currently teaching a course where my students and I are all using Python 3.7 and the current Pygame 1.9.6, so unfortunately, I cannot update to the newer development release of 2.0.  I am also writing a book on OOP using Pygame, and that is currently dependent on the same Pygame release.

Terry:  I tried following your steps.  I opened the appropriate file (idlelib.filelist), and added the line at the appropriate place.  But when I go to save, I get a message:

[Errno 13] Permission denied: 'Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/idlelib/filelist.py'

So I cannot save the file.

I tried opening the same file a simple text editor, BBEdit, and made the same change.  When I went to save I got a message:

Are you sure you want to unlock filelist.py?  You aren't a member of the group 'wheel'.
      Cancel   Unlock

I chose Unlock, saved and quit.  The Finder shows a new date for the file.  But when I double clicked on my Python 3.7 icon, or if I double click on any Python file, IDLE no longer opens.  

I went back into BBEdit, removed the new line, saved again.  Now I can open IDLE as before.  

I don't have a good feel for what files I am supposed to be "allowed" to edit, so I don't know what to try next.  If you have any suggestions about how I can add your debugging line successfully, I'm happy to help.