With a current Tcl/Tk built from the tk-cocoa-8-5-backport branch on OS and a Python that dynamically links with it, attempting to use clipboard copy in Python IDLE's causes Tk to crash. A more general problem with clipboard copies in Text widgets was reported in #3555211 (https://sourceforge.net/tracker/?func=detail&aid=3555211&group_id=12997&atid=112997) which was addressed in Fossil checkin 2fe193d134 on 2012-08-07 (http://core.tcl.tk/tk/info/2fe193d134). That checkin resolved some of the crashes but crashes with IDLE still remain. By the way, it appears that the original clipboard copy regression (as reported in #3555211) was introduced by fossil checkin 90d4b8b59c of 2012-07-25 (http://core.tcl.tk/tk/info/90d4b8b59c).
The orginial problem documented in #3555211 was first noticed with the release of ActiveTcl 188.8.131.52. ActiveTcl 184.108.40.206 apparently includes checkin 2fe193d134 and exhibits the problem documented in this issue as still seen with current tip. The previous ActiveTcl version 220.127.116.11 does not exhibit this problem with IDLE.
To reproduce, install either the current OS X ActivePython 2.7.2 (http://www.activestate.com/activepython/downloads) or an OS X 64-bit/32-bit python.org python (http://www.python.org/download/), install Tcl and Cocoa Tk 8.5 in /Library/Frameworks, launch IDLE (for example, type /usr/local/bin/idle2.7 in a shell). Then when the IDLE PyShell menu appears, use the mouse to doubleclick on some text in the PyShell window (for example "copyright"), then use the mouse to select Edit -> Copy from the menu bar. Using a debug build of Cocoa Tk at current tip (77b3f433c7), the crash occurs at TkpMakeWindow + 465 (tkMacOSXEmbed.c:169). See the attached crash dump. Further observations: The crash seems to only occur using the ActivePython 2.7.2 when selecting the Edit->Copy menu item (and not by using its keyboard accelerator Command-C) and only occurs if no other clipboard copies have succeeded; that is, if you use Command-C first, then Edit->Copy does not cause a crash. Behavior with at least some python.org Python 3.3 (tested with 3.3.0rc1) is different in that the crash occurs using either Command-C or Edit->Copy, unlike 2.7 where only Edit->Copy crashes.