Java Python Integration

Java Python Integration

Why not use Jython? The only downside I can immediately think of is if your library uses CPython native extensions.

EDIT: If you can use Jython now but think you may have problems with a later version of the library, I suggest you try to isolate the library from your app (e.g. some sort of adapter interface). Go with the simplest thing that works for the moment, then consider JNI/CPython/etc if and when you ever need to. There's little to be gained by going the (painful) JNI route unless you really have to.

Integrate python scripts within Java

So actually this is quite simple to do with Java having this built in from the box.

Java has this thing that is called 'ScriptEngineManager'. To use it you just do the following:

ScriptEngineManager sem = new ScriptEngineManager ();
ScriptEngine se = sem.getEngineByName ( "python" );

Now there are a few ways to runa script. Simple call the se.eval () method. You can give this either a String or a Reader and this way it will run the script.

Now to make it have some variables simply use the se.put method. You need to give this two parameters; a String and an Object.

For example:

se.put ( "entity", entity ); // with entity being defined earlier

The onlt thing to keep in mind is that this script manager does not have built in python support. You need to either create your own ScriptEngine for this or use third party software. I found jython and this seems to be working prety well. If you download the standalone jar and put that in your classpath it works. No need for any function calling.

Now in the Script you can call any public member of entity. All the objects, values and those sub-objects get passed through to the script.

My end-code:

Entity class

public class Entity {

String source =
"entity.loc_x += 1\n" +
"entity.loc_z = entity.loc_x";
ScriptEngine se;

loc_x = 0;
loc_y = 0;
loc_z = 0;

public Entity () {
ScriptEngineManager sem = new ScriptEngineManager ();
se = sem.getEngineByName ( "python" );
se.put ( "entity", this );
}

public void update () {
se.eval ( source );
}
}

I hope I helped anyone with this. It was pretty fun tinkering with all of this.

How pyspark integrates with java?

Spark specifically uses Py4J for passing the python application code to run on the JVM. You can find more information here https://www.py4j.org/

You can find the internal architecture here https://cwiki.apache.org/confluence/display/SPARK/PySpark+Internals

Java and Python Integration using Jep

When Jep converts a Python object into a Java object if it does not recognize the Python type it will return the String representation of the Python object, see this bug for discussion on that behavior. If you are running the latest version of Jep(3.8) you can override this behavior by passing a Java class to the getValue function. The PyObject class was created to serve as a generic wrapper around arbitrary python objects. The following code should do what you want:

Jep jep = new Jep();
jep.eval("import pickle");
jep.eval("clf = pickle.load(open('C:/Downloads/DSRFmodel.pkl', 'rb'))");
jep.eval("print(type(clf))");
Object randomForest = jep.getValue("clf", PyObject.class);

jep.eval("import integration");
jep.set("arg1", requestId);
jep.set("arg2", randomForest);
jep.eval("result = integration.trainmodel(arg1, arg2)");

Integration of Java and Python Code in One Eclipse Project

You can keep things in separate projects without having to copy the .class files to the Python project provided that you make that project a PyDev project and add the place that contains the .class files (i.e.: bin folder) as a source folder in the PyDev configuration (and reference that project from your Python project).

Take a look at "Project reference for Jython users" (in the end of http://pydev.org/manual_101_project_conf2.html).

I think you could also do what you asked in your question: create a java project, set it as a PyDev project too (right click that project > pydev > set as pydev project) and configure the PyDev project properties setting the PYTHONPATH to the place where you have your Python files and add another entry to the bin folder (i.e.: where the .class files exist). Not sure if it'd be better to keep those as 2 separated projects though.

Python - Best way to integrate Java GUI and python code

I would do it like this:

Process p = Runtime.getRuntime().exec("python app.py");

You can also pass arguments into the python program as command line arguments, like this:

Process p = Runtime.getRuntime().exec("python app.py arg1 arg2");

Calling Python in Java?

Jython: Python for the Java Platform - http://www.jython.org/index.html

You can easily call python functions from Java code with Jython. That is as long as your python code itself runs under jython, i.e. doesn't use some c-extensions that aren't supported.

If that works for you, it's certainly the simplest solution you can get. Otherwise you can use org.python.util.PythonInterpreter from the new Java6 interpreter support.

A simple example from the top of my head - but should work I hope: (no error checking done for brevity)

PythonInterpreter interpreter = new PythonInterpreter();
interpreter.exec("import sys\nsys.path.append('pathToModules if they are not there by default')\nimport yourModule");
// execute a function that takes a string and returns a string
PyObject someFunc = interpreter.get("funcName");
PyObject result = someFunc.__call__(new PyString("Test!"));
String realResult = (String) result.__tojava__(String.class);

As of 2021, Jython does not support Python 3.x



Related Topics



Leave a reply



Submit