Good morning, Prof.
What you need to understand is that there are certain places that Python looks for modules to import: the entire disk is not searched. The key to your problem is having the interpreter start up in the "current working directory" - the directory where you are working on your script.
I'm not a Mac guy, but it sounds like you, at one time, where able to make your "desktop" look like the current working directory when Python was started.
The trick is to let IDLE handle all of this stuff in the beginning.
- Edit and save files - someplace better than the desktop
- Use the Run menu:Run module command to run your script
- Leave importing at the >>> prompt for much later
Hope that helps.