After looking through the code and experimenting a bit, I propose the following:

The "editor-on-startup" config option should be removed. Running IDLE without arguments should open a shell. If IDLE is asked to open any files for editing, it should open just editor windows. IDLE should open both a shell window and one or more editor windows only when explicitly asked to do so on the command line.

If this is done, the -e option ("open an editor") would tell IDLE to open an empty editor window if no files are asked to be opened for editing. If no other arguments are given, IDLE will open just an editor window (no shell window). The -i option ("open a shell") would tell IDLE to open a shell window even if asked to open files for editing.

I think this is more obvious and easier to work with. It will also make the command line argument processing code simpler. And as a bonus we remove a config option :)

Thoughts? Comments? If there is agreements I will work up a patch.