Jython

http://brendel.com @BrendelConsult

Considering Jython

Juergen BrendelBrendel Consulting


Jython

http://jython.org


Good reasons for Jython

Minimize pain for Java organization

Access to Java class library

Embed in Java app servers

Mix and match Python and Java code


Java is fast

No GIL! Multi-threading uses multiple cores

Object creation is faster

Much faster that cPython in number crunching


Jython% jythonJython 2.5.1 (Release_2_5_1:6813, Sep 26 2009, 13:47:54) [Java HotSpot(TM) Server VM (Sun Microsystems Inc.)] on java1.6.0_20Type "help", "copyright", "credits" or "license" for more information.>>>

You get a standardPython shell


Jython

>>> from java.util import HashMap>>>

Very easy to import any Javaclasses you have in your classpath


Jython

>>> from java.util import HashMap>>> >>> h = HashMap()>>> h['foo'] = 123>>> print h{foo=123}>>> Java's HashMap easier

to use in Python thanin Java!


Jython

>>> from java.util import HashMap>>> >>> h = HashMap()>>> h['foo'] = 123>>> print h{foo=123}>>>>>> type(h)<type 'java.util.HashMap'>>>>


Jython

>>> from java.util import HashMap>>> >>> h = HashMap()>>> h['foo'] = 123>>> print h{foo=123}>>>>>> type(h)<type 'java.util.HashMap'>>>>>>> d = dict()>>> d.update(h)>>> print d{u'foo': 123}


Using Java classes: Easy

public class Foo{ public String stuff(int x) { String buf = new String("Test from Java: ");

buf = buf + Integer.toString(x); return buf; }} So, you write your own

Java code. Here's a simpleclass.



>>> import Foo>>> f = Foo()>>> type(f)<type 'Foo'>>>>

Easy to use fromwithin Python



>>> import Foo>>> f = Foo()>>> type(f)<type 'Foo'>>>>>>> f.stuff(123)u'This is a test from Java: 123'>>>



>>> class Bar(Foo):... def blah(self, x):... print “Python, about to do Java”... print self.stuff(x)... print “And back to Python!”>>>

Now we inherit fromthe Java class...

... in Python!

Call some of thisobject's Java methods.



>>> class Bar(Foo):... def blah(self, x):... print “Python, about to do Java”... print self.stuff(x)... print “And back to Python!”>>>>>> b = Bar()>>> b.blah(123)Python, about to do JavaThis is a test from Java: 123And back to Python!>>>


Use Python in Java?

public class Foo{ ...

public String className(Object x) { Class c = x.getClass(); return c.getName(); }

...}


Use Python in Java?

>>> f = Foo()>>> f.className(123)u'java.lang.Integer'>>>


Use Python in Java?

>>> f = Foo()>>> f.className(123)u'java.lang.Integer'>>>>>> f.className(dict())u'org.python.core.PyDictionary'>>>

On the Java side yousee Java types or someJava representation of

the Python object


Your Python in Java?


Your Python in Java?● Java likes it static!



● Create static contract in Java:class

abstract class

interface



● Create static contract in Java:class

abstract class

interface

● Inherit Python class from that

Only then does yourPython become usable

from within Java,and only the parts that have

been statically declared.


Create Python in Java



Yikes!Using Python fromwithin Java is mucheasier than creating

Python objects.



// Get the handle on the Jython interpreterPythonInterpreter interp = new PythonInterpreter();

// Tell Jython to import something from our Python packageinterp.exec("from test_package import MyPyFooBar");

// Get the object representing the Python classPyObject pyObjectClass = interp.get("MyPyFooBar");

// Instantiate an object of that class. Arguments to __call__() are the wrapped // arguments to __init__()PyObject pyObject = pyObjectClass.__call__(new PyString("String passed in from Java"));

// Convert notsouseful PyObject to an instance of the Java interface classFooBarInterface javaObject = (FooBarInterface)pyObject.__tojava__(FooBarInterface.class);

// Now the object can be used just as if it were a native Java objectString result = javaObject.foobar("some", "arguments", 123);System.out.println("Received from Python: " + result);

Basically, use somecopy and paste to get this

right...


More points to remember

java.lang.Exception != exceptions.Exceptions

Lots of fun when youforget that.


More points to remember

No dynamic import of Java classes

(eval() or conditional import)


The End

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Jython

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