[Jython-users] JSR-223, Jython 2.5.1 and implementing Java Interfaces from Python

[Christian B. <chr...@zy...>]

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Hi there,

TL;DR: Calling methods from an embedded Jython script does nothing when
using JSR-223 and Jython 2.5.1, while Jython 2.2.1 just works fine.

[Disclaimer: This is my first post on this list, so please go easy on me
:-)]

I'm currently trying to switch to Jython 2.5.1 from 2.2.1 and I'm having
a real hard time getting it to work...
Naively, I would've thought that replacing jython.jar with a new one
from 2.5.1 and removing jython-script.jar would just work.
I'm using the JSR-223 interface to embed the scripting engine. By
itself, everything seems to work as expected and the same way as in
Jython 2.2.1 (apart from the newer language that is).
The only thing that is not working for me is implementing a Java
interface from Python and calling methods on it. I have created a small
test program for this:

- ------------- myscript/ScriptingTest.java -------------
package myscript;

import java.io.InputStream;
import java.io.InputStreamReader;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;

public class ScriptingTest {
    public static void main(String[] args) {
        try {
            final ScriptEngineManager manager =
                new ScriptEngineManager();
	    final ScriptEngine engine =
                manager.getEngineByName("python");
	
	    final InputStream is =
                ScriptingTest.class.getResourceAsStream(
                        "/myscript/myscript.py");
            engine.eval(new InputStreamReader(is));
        } catch (final Exception e) {
            e.printStackTrace();
        }
    }
}
- ------------- myscript/PythonCallable.java -------------
package myscript;

public interface PythonCallable {
    String getAString();
    void callAVoid();
}
- ------------- myscript/myscript.py -------------
from myscript import PythonCallable as PythonCallable

class MyPythonCallable(PythonCallable):
    def getAString(self):
        return 'A string'

    def callAVoid(self):
        print 'Called a void method'

print 'getAString() returns: %s' % \
    MyPythonCallable().getAString()
print 'callAVoid():'
MyPythonCallable().callAVoid()
- ------------------------------------------------

Using Jython 2.2.1, I get:
  $ java -cp .:jython.jar:jython-engine.jar myscript.ScriptingTest
  getAString() returns: A string
  callAVoid():
  Called a void method

This is just the way I would expect things to behave (OT: embedding
JavaScript and using a similiar script gives similiar output).

Using a Jython 2.5.1 JAR, as created by the installer (with the default
options), I get this instead:
  $ java -cp .:jython.jar myscript.ScriptingTest
  getAString() returns: None
  callAVoid():

I also tried Jython 2.5.2 RC2 with the same result.

If it matters: my environment is Debian Linux 5.0 AMD64 with the Sun
Java 1.6 JVM, Windows seems to behave the same way.

Am I doing something fundamentally wrong? Is using JSR-223 this way
supported at all in Jython 2.5.1? If I missed relevant documentation,
can somebody point me in the right direction?

Cheers,

- -- 
Christian Blichmann

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