No flame wars please. I am admittedly no fan of Java, but I consider the JVM to be a fairly decent and well-optimized virtual machine. It's JIT-enabled and very close to the common denominator of the prevalent CPU architectures. I'd assume that the CPython runtime would be farther from the metal than a corresponding JVM-based runtime.

If my assumptions are correct, could someone explain to me why Jython suffers such a major loss in performance compared to CPython? My initial assumption was that the JVM was simply designed for static languages, and it was difficult to port a dynamic one to it. However, Clojure seems to be an counterexample to that line of argument.

On the other hand, IronPython seems to be doing fine. I believe the the lead developer on both projects were/are the same, so the argument that code design and implementation in one is significantly better than the other does not seem likely.

I can't figure out what the precise reason is; any help will be appreciated.