Source

jython / README.txt

Full commit
Welcome to Jython 2.1
=======================

Important: The format of both compiled ($py.class) and frozen module
has changed from version 2.0. It is necesary to delete existing
$py.class files and recompile frozen applications when upgrading
to Jython-2.1.

Other backward incompatible changes include:

- The case of module names are now important, even on case ignoring
  filesystems like windows. This matches CPython behaviour.