This can probably be fixed by setting this key in the app's info.plist file: 

<key>NSHighResolutionCapable</key>
<true/>

Under the hood, Tkinter/Tk-Cocoa uses CoreText to render text, and I understand this to adapt to high-res displays out of the box--as long as the proper key is set in the plist file. 

Only pixmaps/images require special developer handling to display properly on Retina displays. As IDLE does not use any such graphics, it should be fine. 

Can someone file a patch for the info.plist file, or at try editing the app's info.plist file and then testing on a high-res display? I do not have access to a Retina display machine on my system. Here are more details on how to enable the key and test it:

http://apple.stackexchange.com/questions/53717/how-does-eclipse-work-on-new-retina-macbook-pros