I have little experience posting in forums, so if this post is in the wrong place, please let me know. 

I am running Python3.9, with Apple OS 10.15.7
I was using IDLE successfully for a class in Python for the past three weeks, although I was rarely able to open a file by double clicking it. It actually worked a few times, but most of the time, nothing happened, and I would open IDLE first, and then open a file from its file menu. 

But today, IDLE will not open. When I click on the icon in the dock like I usually did, it seems to open for about .5 seconds, and then quits. Also, now when I double click on a .py file, IDLE will open for about .5 seconds and then quits. I reinstalled the package, but no change.

However, in terminal I can launch python with this command: python3.9. Then I can launch IDLE with this command: import idlelib.idle. The IDLE window opens, and I can open files from the file menu and they run as before. However, the title of the file menu is now "Python" where before, it was "IDLE"