idle Break as well as Replaces python - Thanks to Jakub Wilk for pointing it out.

debian/changelog

@@ -2,7 +2,7 @@ python-defaults (2.7.2-11) UNRELEASED; urgency=low
 
   * Bump minimum debhelper version to 8 so all tests will run
     - dh_python2 tests 1 - 5 require dh 7 and test 6 needs dh 8
-  * Move idle.xpm symlink from python to idle and add Replaces
+  * Move idle.xpm symlink from python to idle and add Breaks/Replaces
 
  -- Scott Kitterman <scott@kitterman.com>  Wed, 21 Mar 2012 18:40:43 -0400
 

debian/control.in

@@ -67,6 +67,7 @@ Architecture: all
 Depends: ${misc:Depends}, python (= ${binary:Version}), python-tk (>= 2.4.3-3), idle-@PVER@
 Enhances: python
 Replaces: python (<< 2.7.2-11~)
+Breaks: python (<< 2.7.2-11~)
 Description: IDE for Python using Tkinter (default version)
  IDLE is an Integrated Development Environment for Python.
  IDLE is written using Tkinter and therefore quite platform-independent.