Running Python modules in Python, from Jython

Question

I have been dropped into a complicated environment, where I am working with a Python library but everything else we have is in Java. We want to be able to access and use the Python library from Java, so we started researching and using Jython.

Jython is pretty great, and we are importing the Jython Interpreter into our Java program so that we can access most of the library. However, Jython doesn't quite support everything, and there's not much we can do to get around that. All the paths are set up correctly and there are some modules that we just can't import.

So assuming that there's nothing else we can do to make the Python library Jython-compatible, the next idea is to somehow invoke Python from the Jython interpreter, and make Python run a module (written in Python). Ideally, we would be able to simply import the module using Python, and then call all the methods using Jython (but have them executed in Python).

Does anyone know if this is possible at all, and if so how?

Answer 1

You should be able to use Pyro to send method calls and their return data between Jython and CPython. It's designed so that "objects can talk to each other over the network" but there's no reason the same technique shouldn't work between two different types of Python on a single machine.

In the Pyro documentation you will find a simple example which shows you just about everything you need to know to get this up and running.

Answer 2

You should take a look at

• JEP (https://github.com/mrj0/jep) or
• JPY (https://github.com/bcdev/jpy).

Both are frameworks designed exactly for the purpose you demand. Also keep an eye on JyNI (www.jyni.org) which is still in an early state, but will vastly improve Jython-support for a vast amount of Python-frameworks.

Using Pyro (https://pypi.python.org/pypi/Pyro4) you will probably also be able to solve your task, but keep in mind that it was not actually designed for this purpose but for distributed network stuff. This can yield subtle issues (e.g. poor performance) rendering it an edgy solution. This must not necessarily be the case, but I would recommend to prefer a solution intended for a task if one is available. However take this just a hint and humble warning as I did not actually compare the named approaches in practice.

Answer 3

You can avoid Jython altogether and still talk to python via Pyro, by using Pyrolite in your Java code. Pyrolite is a lightweight client library that lets your java program talk directly to Pyro. Will work as long as your java program is only a Pyro client.