I am glad to see this. Gregor has been inactive for several years, Except for Ned's recent patch for OSX, it has been years since there was a turtle-specific code patch (from hg revision history).

Questions: is there project link? are any of the mentors core developers, with commit rights? or would you need commits from someone like me?

I have read turtle.py and found that the multiple layers made some things hard to follow. To me, this was a bigger impediment than code formatting. You may want to develop an outline of the layer structure.

As you may know, Guido generally discourages pure code cleanups and prefers that they be done when the code is examined for other purposes. I personally think some changes are safe enough if verified by a second person.

I looked for and did not fine test/test_turtle. Did I miss something? Turtledemo is a partial substitute, but it might not exercise all turtle functions.

If you only apply cleanups to 3.5, subsequent bug fixes for all 3 versions will become much more difficult. The default commit process assumes that maintenance patches merge forward cleanly. I try to keep Idle code the same across versions as much as possible.