First it was IKVM, which can JIT compile JVM bytecodes to CLR bytecodes. Now commenter Paul Boddie has written javaclass, which aims to do a similar thing with the Python bytecodes as a target:

The javaclass collection of packages and utilities (also known as ClassFile) provides a means of importing Java classes and packages directly into Python, without the need for a Java virtual machine, so that the classes may be instantiated, accessed, run and manipulated just like Python classes, and that the resulting objects and methods can be accessed and manipulated just like Python objects and methods. It should be possible to run compiled Java programs with the Python interpreter and not notice that it isn't the Java virtual machine being used - given sufficient library support for the program concerned, of course.