Jython 2.7 and techniques for integrating with Java - Frank Wierzbicki

Jython 2.7 Update
Frank Wierzbicki

Wednesday, May 9, 2012

Why use Jython?

• Massive amounts of Java code out there
• Some really useful Java libs
• Great JVM ecosystem
• But we’d all rather be writing Python code,
right?


Status
• Jython 2.7 is progresing well
• bytearray and io are the last missing big
features
• 2.7 Unit test compliance
• 684 failing tests out of 10786 (~6%)
• Most of these are due to bytearray/io

Dates

• Jython 2.7 work is being sponsored by
Adconion. (Thanks!)
• Jython 2.7 alpha should be out this month
• The target for a production release is July
15 - which happens to be the ﬁnal day of
my contract to get Jython to 2.7 :)


Why is Adconion
sponsoring Jython?
• Adconion is a hybrid Java/Python shop
based out of LA
• They use Python version 2.7 and Jython 2.5
• They have internal Django apps that access
Java libraries
• The 2.5/2.7 differences are a pain
• They’d like to give back to the community

Collaborators
• Major apps
• Implementations - CPython, PyPy
• Other Java dynamic languages - JRuby
• Tooling support
• Java Virtual Machine development
• Academic research - gradual typing

Features
• Abstract Base Classes
• Bytearray
• __format__
• OrderedDict
• lots of Lib updates
• See CPython 2.6/2.7 what’s new for more

Not in Jython 2.7

• multiprocessing
• buffer (so far never has been in Jython)
• memoryview (though there is a start, we’ll
see)


java.util.concurrent
not interpreted

Java Platform
no GIL

-J for setting options
like one of 20 or so GCs
heap size
etc

• Starting to (optionally) use invokedynamic
• Everything is compiled to Java Bytecode
• Use a choice of Java garbage collectors
• Always uses Java native threads
• All cores are used


Java Integration

• Jython integrates well with Java
• Jython makes calling into Java look like
standard Python code
• Java classes and interfaces can be
subclassed from Jython


builtin Java interfaces

• Jython’s list implements Java List<Object>
• Jython’s dict implements Map and
ConcurrentMap
• Jython’s set implements Java Set


//Java interface
package org.acme;

public interface MyInterface {
public List strList();
}

#From Python in file “acme.py”
from org.acme import MyInterface

class pyobject(MyInterface):
def strList(self):
return [‘a’, ‘b’, ‘c’]

//From Java
PythonInterpreter interpreter = new PythonInterpreter ();
interpreter.exec ("from acme import pyobject");
MyInterface pythonObject = interpreter.get ("pyobject");

List pywords = pythonObject.strList()
for (Object o : pyList){
String string = ((PyObject)o).__toJava__(String.class);
//Do something with the now Java native strings.
}


PlyJy

• For a more sophisticated approach to
calling into Python code from Java in Jython
see the PlyJy project


import org.plyjy.factory.JythonObjectFactory;

JythonObjectFactory factory = JythonObjectFactory.getInstance();
MyInterface pythonObject = (MyInterface) factory.createObject(
MyInterface.class, "acme.pyobject");


Jython package cache
[frank jython]$ ./dist/bin/jython
*sys-package-mgr*: processing new jar, '/home/frank/hg/jython/jython/dist/jython-dev.jar'
*sys-package-mgr*: processing new jar, '/home/frank/hg/jython/jython/dist/javalib/antlr-2.7.7.jar'
*sys-package-mgr*: processing new jar, '/home/frank/hg/jython/jython/dist/javalib/antlr-3.1.3.jar'
*sys-package-mgr*: processing new jar, '/home/frank/hg/jython/jython/dist/javalib/antlr-runtime-3.1.3.jar'
*sys-package-mgr*: processing new jar, '/home/frank/hg/jython/jython/dist/javalib/asm-4.0.jar'
*sys-package-mgr*: processing new jar, '/home/frank/hg/jython/jython/dist/javalib/asm-commons-4.0.jar'
...


Java package cache
• Goes through all jars and classes and
ﬁgures out Java package contents
• enables “from java.foo import *”
• Java does not have a package.getClasses()
• If cache is disabled “from java import *” will
not work from Jython
• * import for pure python still works

zxJDBC

• zxJDBC implements DB-API
• integrated into Jython’s core
• A crucial piece for SQLAlchemy, Pyramid
and Django support.


Modjy

• Modjy implements WSGI for Jython
• Acts as a bridge to Java Servlets
• integrated into Jython’s core
• Pyramid and Django support


Working apps
• SQLAlchemy
• Pyramid, DJango
• setuptools, ez_install, distribute
• virtualenv
• pip
• many more pure python apps

ez_install

• Get ez_setup.py
• run “jython ez_setup.py”
• In Jython’s bin directory will be an
ez_install that runs from Jython


Install Django
• Get 1.3+ Django - run “jython setup.py
install”
• From http://django-jython.googlecode.com
get django-jython-1.3.tar.gz, untar it and run
“jython setup.py install”
• see the django-jython project on
googlecode.com for more detail


Deploy Django

• run “jython manage.py war --include-java-
libs=jdbcdriver.jar”
• This will produce a “war file”
• Copy this war file to the auto-deploy
directory for most application servers (like
Tomcat, Jetty or Glassfish)


Pyramid on Jython

• jython ez_install pyramid
• Note that you should not try to use
Chameleon with Jython - use Mako for
templates.


Creating an executable
Jar
• Make a copy of jython.jar
• copy Lib/ into jython.jar
• copy a __run__.py ﬁle into new jar
• in the future it will be a __main__.py to ﬁt
with the new CPython convention as of
2.6/3.0


Add Jython install stuff
to a new jar
$ cd $JYTHON_HOME
$ cp jython.jar app.jar
$ zip -r app.jar Lib


Add modules and paths
to the jar ﬁle
$ cd $MY_APP_DIRECTORY
$ zip app.jar *.py
# Add path to additional jar ﬁle.
$ jar ufm myapp.jar othermanifest.mf
#Where, othermanifest.mf contains the following:
Class-Path: ./otherjar.jar


Add runner ﬁle, and
run!
$ zip myapp.jar __run__.py
#in 2.7/3.x
$ zip myapp.jar __main__.py
$ java org.python.util.jython -jar app.jar


Jython 3000
• We already have a Jython 3 branch
• It has a nearly complete parser
• Not much else yet
• Can’t wait to delete old style classes and
fake str suppot!
• I’d like to target 3.3 and support only JDK7
or above (maybe even JDK8 if it takes long)


Jython 3 changes?
• All of the same changes as Python3
• unicode for all strings
• no old style classes
• new metaclass syntax
• many iterators instead of lists
• much more

Jython speciﬁc changes

• Better way to call into Jython? Project
Lambda maybe?
• Default to not scan packages?
• Get rid of swing speciﬁc helper functions
• Remove Lib gunk


Jython/CPython
collaboration
• Break out the CPython standard Lib into a
shared Lib - merge all of Jython’s
customizations into CPython Lib
• Share CPython’s 3.3 import implementation
• PEP 420 implicit namespace packages for
Java packages


Where to Find Out
More
• http://www.jython.org
• http://wiki.python.org/jython
• http://fwierzbicki.blogspot.com
• Twitter: fwierzbicki
• frank@python.org


Jython 2.7 and techniques for integrating with Java - Frank Wierzbicki

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