Jython is a Python interpreter implemented in Java. It allows Python code to integrate with Java by compiling Python code to Java bytecodes, making all Java classes immediately available to Python code. This allows Python to call Java code and Java to call Python, enabling flexible scripting of Java applications and experimentation in an interactive Java environment.

1. Jython: Integrating
Python and Java
Charles Anderson
Western Skies Consulting
Western Oregon University
charles@western-skies.us / andersc@wou.edu

2. 10 Second Summary
• Jython is the Python interpreter
implemented in Java

3. Outline
• Python
• Scripting and embedded languages
• Jython
• Other Java scripting languages

4. Python Background
• Python is a object-oriented scripting
language - runs on many platforms
• Mature but still evolving: version 1.0 -
1994, current version: 2.5, 3.0 under
development
• Huge user base including Google,Yahoo,
YouTube, Industrial Light & Magic

5. Python Overview
• Python is a scripting language - no compile
• Dynamic typing - no variable declarations,
but strictly typed at runtime
• Simple syntax - large library rather than
cryptic syntax (c.f., Perl)
• Often a refuge from other languages

6. Hello World
• print “hello world”
• that’s it - no semicolons, no main function,
no curly braces, etc.

7. Language Features
• Object oriented: hybrid/not pure, multiple
inheritance - c.f., C++
• Polymorphism without inheritance - “duck
typing”
• Very dynamic - introspection/reflection is
simple and powerful - c.f., Java

8. Syntax
• Pretty simple - familiar to Java programmers
c = sqrt(a*a, b*b)
emp = Employee(‘Bob’, ‘Jones’)
employees[‘Bob’] = emp
import sys, email.mime.text

9. More Syntax
if x < 0:
print ‘negative’
try:
z=y/x
except ZeroDivisionError, msg:
print msg

10. Class Definition
class Point2D:
def __init__(self, x, y):
self.x = x
self.y = y
def distance(self):
return math.sqrt(
self.x**2+self.y**2)

11. Syntax Notes
• The block structure of code is determined
by indentation - what you see is what the
compiler sees
• No dangling curly braces
• Python favors libraries over fancy, terse
syntax - c.f., Perl
• When needed, __method__

12. Embedded Languages
• TCL was developed to provide a common
command language for tools written in C
• Adding command line to tools
• Extending TCL to add commands from C
to TCL
• Similar to Unix shell - C functions instead
of executable programs

13. Extending TCL
• TCL uses a simple interface between TCL
and C code: int argc, char** argv
• Programmer writes thin layer of interface
functions to expose functionality to TCL
• Programmer has to choose functions to be
exposed
• Can be automated - swig

14. Scripting a Program
• Do the real work in C (or whatever) and
glue it together with TCL
• Provides extensibility of C tool to users
• Performance of script language doesn’t
really matter - Pareto principal
• E.g., Numeric Python at LLNL
• Can prototype in scripting language

15. Python Interpreter
• Python is an interpreted language - need an
interpreter to execute Python code
• Originally written in C - “CPython”
• Code is compiled to byte codes at runtime
• Python can be interfaced with existing C
code similar to TCL

16. Jython Interpreter
• Jython is Python interpreter written in Java
• Python code is compiled to Java byte codes
• Aside: Iron Python is interpreter written
to .Net CLR

17. Jython Ramifications
• Interpreter written in Java - so what?
• Jython interfaces directly to Java w/o any
explicit coding
• Uses Java introspection/reflection
• All Java classes on class path are immediately
available from Python code
• Interactive command line for Java

18. Demos
• Interactive
• GUI

19. Java Python Integration
• Python can call Java code
• Java code can call out to Python - possibly
in a new Python interpreter (sandbox)
• Python code can sub-class Java classes

20. Possible Uses
• Command prompt for controlling app
• Interactive workbench for experimenting
• One-off utility work - e.g., data loading
• Flexible “business” rules

21. Scripting Java
• Groovy - groovy.codehaus.org
• JACL (TCL in Java) - tcljava.sourceforge.net
• JRuby - jruby.codehaus.org
• JSR 223 Scripting the Java Platform -
Java 6 SE

22. Jython Information
• www.jython.org
• There are a couple of Jython books
• “Scripting: Higher Level Programming for
the 21st Century” - Ousterhout