ttk is not available with 8.4 (except maybe with the tile extension, but I believe some changes were made before it was incorporated in 8.4 as ttk). As I mentioned on the ttk thread on idle-sig, it was agreed in a pydev discusion a couple of years ago or so that Idle could use ttk widgets and thereby require 8.5. 8.5 is about 8 years old. Tracker issues and pydev discussion about using ttk in Idle go back at least 5 years.  Two examples of the latter are "IDLE contributors and committers" and "Removing IDLE from the standard library" from July 2010. G. Polo's patches using ttk were part of the discussion.

Mark Roseman has used tk for 22 years and ttk for at least 8 and written a nice website and book on how to use them (which I have read).  He has offered to help upgrade Idle with ttk. I am excited about taking advantage of the offer.  This will alleviate many of the complaints about Idle's appearance and allow use of the (tabbed) Notebook, and Treeview widgets new with ttk. Even on Windows, the ttk Scrollbar is a noticeable improvement.

I do not want to keep Idle development frozen for the benefit of the few users of the 8-year-old Mac OS 10.5 who might also want to use Idle.  The alternatives I see are removing Idle from the 10.5 release; asking those who want Idle to upgrade to a new ActiveState distribution, if there is one that works on 10.5; or include with that release a frozen version of Idle as it was yesterday, before I applied the first patch importing ttk.

Nick, do you remember any of the pydev discussions, or have any comments?