Communication between Java and Python

TechTalk: Communication between Java and Python Anastasia Eifer, DLR Simulations- und Softwaretechnik 03.06.2008

Contents

Introduction

Motivation

Communication through bindings (JPE, JPI)

Jython (JPython)

Jepp

JPype

Client-server communication (SPYRO, Pyro)

Summary

Introduction (1/4)

Java

Object-oriented

Platform-independent

Robust

Distributed

Secure

One of the most popular programming languages today

Introduction (2/4)

Python

Dynamic multi-paradigm programming language

Object-oriented

Functional

Aspect-oriented

Scripting language

…

Remarkably clean syntax

Short development time

Extensive standard libraries

Highly readable language

Can be learned in a few days

Introduction (3/4)

"Hello World!"-Code

Java

Python

print("Hello World!") public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } }

Introduction (4/4)

Print the integers from 1 to 9

Java

Python

for (int i = 1; i < 10; i++) { System.out.println(i); } for i in range (1,10): print i

Motivation

Java and Python: a perfect couple

Building software from existing components

Combination of a system programming language (Java) and a scripting language (Python)

Rapid application development

Creating automated tests

Embedded scripting

Communication through bindings

JPE

Java-Python Extension

JNI-based wrapper

Integration of Java and standard Python (CPython)

http://jpe.sourceforge.net/

JPE project does not appear to be active

JPI

Java-Python Interface

JNI-based wrapper

JPI project is no longer developed

Jython (1/4)

What is Jython?

Complete re-implementation of the Python programming language in Java

Embedded scripting

Interactive experimentation

Rapid application development

Home

http://www.jython.org

Jython (2/4)

Interactive experimentation

C:jython>jython

Jython 2.0 on java1.2.1

Type "copyright", "credits" or "license" for more information.

>>> from java.util import Random

>>> r = Random()

>>> r.nextInt()-790940041

>>> for i in range(3):

... print r.nextDouble()

...

0.23347681506123852

0.8526595592189546

0.3647833839988137

>>>

Jython (3/4)

Running Python scripts

import org.python.util.PythonInterpreter;

import org.python.core.*;

class TestPython {

public static void main ( String[] args ) { try { org.python.util.PythonInterpreter python =

new org.python.util.PythonInterpreter(); python.execfile ( "testscript.py" ); } catch ( Exception e ) { System.out.println ( "An error was encountered." ); }

}

}

Jython (4/4)

Current state of development

The current release is Jython-2.2.1

It is equivalent to the 2.2 release of CPython

CPython 2.5 is targeted for the next release

Jython-2.2.1 supports a large majority of the standard Python library

Jython-2.2.1 doesn't support a number of Python's built-in modules !

(e.g. those that are written in C for CPython)

Jepp (1/4)

What is Jepp?

Java Embedded Python

Embeds CPython in Java

Communication through interfacing at the native level in both Virtual Machines

Home

http://jepp.sourceforge.net /

Jepp (2/4)

Using Jepp from within Java

„ Hello World!“-Code

Jep jep = new Jep();

jep.eval("print 'Hello World!'");

jep.close();

Jep jep = new Jep(false);

jep.runScript("C:\temp\testscript.py");

jep.close();

Jepp (3/4)

Features

Using the console ( console.py script)

Creating new exception types on the fly

$ java -jar jep.jar console.py

>>> from java.lang import *

>>> s = String('do crazy stuff')

>>> print String(s.toCharArray()[3:8])

crazy

>>> from java.io import FileInputStream

>>> try:

... FileInputStream('no such file')

... except(jep.FileNotFoundException):

... print 'File not found.'

...

File not found.

Jepp (4/4)

Summary

Very good scripting solution for Java

Run your existing Python scripts from Java

Access to high-quality Python extensions

Jepp's console provides an easy way to examine scripts and learn how to use new APIs

JPype (1/3)

What is JPype?

JNI-based wrapper

Communication through interfacing at the native level in both Virtual Machines

Full access to java class libraries

Home

http://jpype.sourceforge.net /

JPype (2/3)

„ Hello World!“-Code

from jpype import *

startJVM(path to jvm.dll, "-ea")

java.lang.System.out.println("Hello World")

shutdownJVM()

JPype (3/3)

import jpype

#start JVM with class path

startJVM(path to jvm.dll, "-ea")

#create reference to java package

javaPackage = jpype.JPackage(" JavaPackageName " )

#create reference to java class

javaClass = javaPackage. JavaClassName

#create instance of java class

javaObject = javaClass()

#call java methods

javaObject. JavaMethodName()

#shutdown JVM

jpype.shutdownJVM()

Client-server communication

SPIRO

Simple Python Interface to Remote Objects

Handy bridge between CPython and Java (via Jython)

http://www.freenet.org.nz/python/spiro

Pyro

Python Remote Objects

http://pyro.sourceforge.net /

Python Interpreter Python Interpreter Java Virtual Machine (JVM) Java Code (Anwendung) Jepp JNI Python Code JPype Jython Python Code Interface/Protokoll Python Code Python Code (Autor: Andreas Schreiber)

Summary