Jython

Considering Jython

Juergen Brendel
Brendel Consulting

http://brendel.com @BrendelConsult

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
% jython
Jython 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_20
Type "help", "copyright", "credits" or "license" for more information.
>>>

You get a standard
Python shell


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

Very easy to import any Java
classes you have in your classpath


Jython
>>>
>>> h = HashMap()
>>> h['foo'] = 123
>>> print h
{foo=123}
>>> Java's HashMap easier
to use in Python than
in Java!


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


Jython
>>>
>>> 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 simple
class.


>>> import Foo
>>> f = Foo()
>>> type(f) Easy to use from
<type 'Foo'> within Python
>>>


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


Now we inherit from
the Java class...
>>> class Bar(Foo): ... in Python!
...     def blah(self, x):
...         print “Python, about to do Java”
...         print self.stuff(x)
...         print “And back to Python!”
>>>
Call some of this
object'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 Java
This is a test from Java: 123
And 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() On the Java side you
see Java types or some
>>> f.className(123) Java representation of
u'java.lang.Integer' the Python object
>>>
>>> f.className(dict())
u'org.python.core.PyDictionary'
>>>


Your Python in Java?


● Java likes it static!



● Create static contract in Java:
class
abstract class
interface



● Create static contract in Java:
Only then does your
class Python become usable
from within Java,
abstract class and only the parts that have
been statically declared.
interface

● Inherit Python class from that


Create Python in Java



Yikes!
Using Python from
within Java is much
easier than creating
Python objects.


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

// Tell Jython to import something from our Python package
interp.exec("from test_package import MyPyFooBar"); Basically, use some
copy and paste to get this
// Get the object representing the Python class
PyObject pyObjectClass = interp.get("MyPyFooBar"); right...

// 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 class
FooBarInterface javaObject =
(FooBarInterface)pyObject.__tojava__(FooBarInterface.class);

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


More points to remember

java.lang.Exception != exceptions.Exceptions

Lots of fun when you
forget that.


More points to remember

No dynamic import of Java classes

(eval() or conditional import)


The End

juergen@brendel.com

@BrendelConsult

http://brendel.com


Jython

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