\subsubsection{Jython}

Jython\cite{Jython} is the most fully developed version of Python available for the JVM.  It consists of a compiler which generates bytecode from arbitrary Python source, and a Java re-implementation of Python's built-in types and native libraries.  

Because Jython generates bytecode for arbitrary Python code, rather
than merely RPython, it cannot use the simple one-to-one class mapping
that the RPython translator uses.  Instead, it's structure is much
closer to an interpreter.  For example, there is a single Java class
for all Python objects, which contains a pointer to another object
that represents the object's type, and field and method lookups are
indirected through a hashtable rather than using the dedicated JVM instructions.

Unfortunately, because the JVM backend is not yet able to translate a full Python interpreter, it is not possible to compare the performance of Jython-generated code with PyPy directly.