jython-users — Discussion of and questions about using Jython

Re: [Jython-users] How to call super class attributes in Python-derived Java classes

[Robert W. B. <rb...@di...>]

On Thu, 25 Oct 2001, Andres Corrada-Emmanuel wrote:
> ...
> I've gone further and confirmed that if my Foo.java code makes the
> attribute public, everything works fine. This seems to contradict the
> Java transparency claim for Jython also:

I think setting python.respectJavaAccessibility to false convinces
even the most reluctant to believe in transparency <g>

-robert

Re: [Jython-users] How to call super class attributes inPython-derived Java classes

[Robert W. B. <rb...@di...>]

On Thu, 25 Oct 2001, Andres Corrada-Emmanuel wrote:
> On Thu, 25 Oct 2001, Kevin Butler wrote:
> > [CC's removed]
> > Andres,
> > You need to explicitly declare the 'outputTags' attribute as public:
> >
> >     public String outputTags;
> >
> > Your existing declaration:
> >
> > >     String outputTags;
> >
> > leaves it 'package-protected' ("friendly"), and subclasses could normally use it just fine, but because Jython attempts to access the attribute from its own package, the field is not visible.
> >
> > kb
>
> Okay. I got that working. But this brings me back to my original problem:
> I have a Python class that subclasses a Java class in a package. How do I
> tell Python that it can access that package's attributes?

I was mistaken earlier about saying there's a difference between package
private fields and methods.  I confused myself into thinking protected
attributes.

Yes, package private attributes are inaccessible. I do not know of a way
to "tell" jython that it can access them other than setting
respectJavaAccessibility to false.

> When I compile the Python class with jythonc I use the --package option
> and can see that the .java file created does have the correct package
> statement but I still cannot see the super's attributes.

You mean just package private attributes and protected fields, right? You
do have access to protected methods and everything public in the
superclass.

> Isn't that problematic?

<opinion>
Not really.  If you are writing the package, you have the power to use
jython-friendly permissions. If someone else wrote the package, chastise
them for making users develop in the same package <g>
You also have the choice to set respectJavaAccessibility to false.
</opinion>

-robert

> Andres Corrada-Emmanuel
> Senior Research Fellow
> Center for Intelligent Information Retrieval
> University of Massachusetts, Amherst

[Jython-users] Package attributes not reachable from Python-derived Java classes

[Andres Corrada-E. <co...@ci...>]

Hello,

My problem has evolved to this thread. Let me recapitulate my intent:

To create a Java class using Python code. The Python class subclasses from
a class in some package "edu.umass.cs.ciir.metamorph".

I compile the Python class to a .class file using jythonc with the
package switch. The resultant .java file has the correct package
declaration:

package edu.umass.cs.ciir.metamorph;

at the top of the file.

My Python class tries to access a package-accesible super attribute but
fails. If I make that attribute public it succeeds. This is
unsatisfactory. I'm trying to use someone elses code and I cannot change
the attribute properties.

Can I still use Jython or do I need to abandon this line of approach and
resign myself to having to program in Java directly?

Andres Corrada-Emmanuel
Senior Research Fellow
Center for Intelligent Information Retrieval
University of Massachusetts, Amherst

Re: [Jython-users] How to call super class attributes inPython-derived Java classes

[Andres Corrada-E. <co...@ci...>]

On Thu, 25 Oct 2001, Kevin Butler wrote:

> [CC's removed]
>
> Andres,
>
> You need to explicitly declare the 'outputTags' attribute as public:
>
>     public String outputTags;
>
> Your existing declaration:
>
> >     String outputTags;
>
> leaves it 'package-protected' ("friendly"), and subclasses could normally use it just fine, but because Jython attempts to access the attribute from its own package, the field is not visible.
>
> kb
>

Okay. I got that working. But this brings me back to my original problem:
I have a Python class that subclasses a Java class in a package. How do I
tell Python that it can access that package's attributes?

When I compile the Python class with jythonc I use the --package option
and can see that the .java file created does have the correct package
statement but I still cannot see the super's attributes.

Isn't that problematic?

Andres Corrada-Emmanuel
Senior Research Fellow
Center for Intelligent Information Retrieval
University of Massachusetts, Amherst

Re: [Jython-users] How to call super class attributes in Python-derived Java classes

[Andres Corrada-E. <co...@ci...>]

Hi Robert,

The files I'm using can be seen at:

http://aspn.activestate.com/ASPN/Mail/Message/Jython-users/819819

I've gone further and confirmed that if my Foo.java code makes the
attribute public, everything works fine. This seems to contradict the
Java transparency claim for Jython also:

-I can write Java classes that use Foo.java and they can access Foo's
attributes without having to make those attributes public.
-A python class can only access explicitly public attributes.

On Thu, 25 Oct 2001, Robert W. Bill wrote:
>
> Is this the random postings from a while back, or something new
> I'm not seeing yet?  I actually have a few minutes to take a good
> look this afternoon rather than the guesses sent so for :)  If you
> could point me to these simple files it would help.
>
> Tnx,
> Robert

The problem with calling java.util.Random's initializer was solved by a
posting made by Finn. This thread is about my next step: getting a Python
class to access package variables. To simplify the problem, I have come up
with the simple files shown in the URL above.

Thanks for your help on this.

Andres Corrada-Emmanuel
Senior Research Fellow
Center for Intelligent Information Retrieval
University of Massachusetts, Amherst

Re: [Jython-users] How to call super class attributes in Python-derived Java classes

[Andres Corrada-E. <co...@ci...>]

On Thu, 25 Oct 2001, Robert W. Bill wrote:

> Hi Andres,
>
> .
> .
> .
> IIRC Jython's indirection causes the actual call in this case to originate
> from the org.python.core package. Methods go through the proxy to act like
> the real package/subclass, but fields do not. In other words, your
> stringArray needs to be public, or you need to write an intermediate/shell
> java class that exposes this field (e.g. a get method).
>

Hi Robert,

I've managed to recreate the problem with simple files that I sent in a
previous posting. It seems that the problem is worse, one cannot access
super class attributes even if one just uses Jython.

This seems to contradict the claim that Jython allows you to use Java
classes transparently so I think I must be missing the correct syntax to
do the work.

Andres Corrada-Emmanuel

Re: [Jython-users] How to call super class attributes in Python-derived Java classes

[Andres Corrada-E. <co...@ci...>]

Hello,

I have simplified my problem of accessing super class attributes to the
following simple files--

Java super class:

public class Foo {
    String outputTags;

    public Foo() {
        outputTags = new String("This is the Foo string!");
    }
}

Python class that subclasses this Foo java class:

import Foo

class Bar(Foo):

    def __init__( self ):
        "Do nothing since jythonc will call Foo's constructor."
        pass

    def testAttributeCall( self ):
        "@sig public java.lang.String testAttributeCall()"
        return self.outputTags

Java file to test jythonc's creation of Bar.class:

import Bar;

class TestAttribute
{
    public static void main(String args[]){
        Bar myBar = new Bar();
        System.out.println( myBar.testAttributeCall() );
    }
}

This fails with:

AttributeError: instance of 'Bar' has no attribute 'outputTags'.

The problem is also present if the Bar.py file is used (with an added
Foo.__init__(self) call) from within Jython.

So the question remains, how does one call super class attributes to
avoid the AttributeError?

Andres Corrada-Emmanuel
Senior Research Fellow
Center for Intelligent Information Retrieval
University of Massachusetts, Amherst

Re: [Jython-users] How to call super class attributes in Python-derived Java classes

[Robert W. B. <rb...@di...>]

Hi Andres,

On Thu, 25 Oct 2001, Andres Corrada-Emmanuel wrote:
> On Wed, 24 Oct 2001, Robert W. Bill wrote:
> > Is the stringArrayInitializedInSuperMethodCalledBefore a protected field?
> > or public?
> >
> > Just curious because field access does not go through the proxy making
> > protected fields == private.
>
> stringArrayInitializedInSuperMethodCalledBefore is defined as "package
> private". I have run jythonc with the --package option set to the super's
> package and confirmed that the package statement is correct in the
> generated .java file. The error still occurs nonetheless: I cannot access
> super class attributes in my Python code (which in turn is converted into
> a .class file).

IIRC Jython's indirection causes the actual call in this case to originate
from the org.python.core package. Methods go through the proxy to act like
the real package/subclass, but fields do not. In other words, your
stringArray needs to be public, or you need to write an intermediate/shell
java class that exposes this field (e.g. a get method).

-Robert

Re: [Jython-users] How to call super class attributes in Python-derived Java classes

[Andres Corrada-E. <co...@to...>]

On Wed, 24 Oct 2001, Robert W. Bill wrote:

>
> Is the stringArrayInitializedInSuperMethodCalledBefore a protected field?
> or public?
>
> Just curious because field access does not go through the proxy making
> protected fields == private.
>

stringArrayInitializedInSuperMethodCalledBefore is defined as "package
private". I have run jythonc with the --package option set to the super's
package and confirmed that the package statement is correct in the
generated .java file. The error still occurs nonetheless: I cannot access
super class attributes in my Python code (which in turn is converted into
a .class file).

[Jython-users] How to call super class attributes in Python-derived Java classes

[Andres Corrada-E. <co...@ci...>]

Hi,

I'm building a Java class from Python code using Jython (jythonc properly
speaking).

My Python code refences an attribute that exists in the Java super class,
something like this:

class MyClass( JavaSuperClass ):
    .
    .
    .
    def foo( self ):
        aStringArray = self.stringArrayInitializedInSuperMethodCalledBefore

This fails with an attribute not found error.

The traceback shows that the jythonc derived class is trying to find the
attribute in the Python side of MyClass, while the attribute is really in
the super class in the Java side.

What is the proper syntax for calling a super's attribute in Python code
that will be turned into a Java class? Thank you.

Andres Corrada-Emmanuel
Senior Research Fellow
Center for Intelligent Information Retrieval
University of Massachusetts, Amherst

Re: [Jython-users] Can one call the super class constructor from a Python class init?

[Andres Corrada-E. <co...@ci...>]

Hi Finn,

Thank you for helping me out on this problem. I'll post my modified
scripts when I get them to work so others can avoid my mistakes.

Andres Corrada-Emmanuel

RE: [Jython-users] jython with xml

[O'Brien-Strain, E. <eo...@ex...>]

Possibly you need to put the jar file for some XML parser on your classpath.

You can get the xerces parser from:

  http://xml.apache.org/xerces-j/

__
Eamonn O'Brien-Strain
HP Labs
eo...@hp...


-----Original Message-----
From: Michael Chermside [mailto:mc...@de...]
Sent: Tuesday, October 23, 2001 7:58 AM
To: jyt...@li...
Subject: [Jython-users] jython with xml


Hoping someone can help:

I wrote a quick prototype in cpython for my project; but now I'd like to 
compile with jython and run under java. My program uses some things from 
the xml package. At first, I was worried that it wouldn't be possible 
(no parser), but as I was reading xml.sax.__init__.py, I saw that it has 
special casing for the java environment.

1) Can I run something using the xml parser under jython?

2) If so, then what am I doing wrong? I have been setting sys.path to 
include my python 'libs' directory, then importing my package. I get an 
exception:
   File "C:\Applications\Python21\lib\xml\sax\__init__.py", line 88, in 
make_parser
   SAXReaderNotAvailable: No parsers found

This looks bad, but the special-case code must be there for some reason.

Anyone able to help?

-- Michael Chermside


_______________________________________________
Jython-users mailing list
Jyt...@li...
https://lists.sourceforge.net/lists/listinfo/jython-users

Re: [Jython-users] Error when attempting to create a Proxied object with a constructor

[<bc...@wo...>]

[Max Muller]

>Hi,
>	So I've got the PythonInterpreter running inside my Java app  
>(thanks to everyone for the pointers to PyServlet example) and I  
>successfully get a Proxied class object from this bit of code  that  
>looks something like:
>
>         interpreter().execfile(testFile.getAbsolutePath());
>	
>	PyObject cls = interpreter().get("Test");
>
>          Object o = cls.__tojava__(Class.class);
>
>	Class testClass = (Class)o;

I don't think we ever tested this when the code was create with
exec/execfile. I believe it works when the python code is placed in a
module. The proxy tries to import the module that the code was compiled
from.

Do you really need to call the java Constructor directly? Normally it it
a lot easier to simple call the python class:

  PyObject instance = cls.__call__(Py.java2py(aWOContext));

regards,
finn

Re: [Jython-users] Can one call the super class constructor from a Python class init?

[<bc...@wo...>]

[Andres Corrada-Emmanuel]

>Apparently the answer is no if you plan to turn that python class back
>into a java class. 

Right.

>Is this a bug or am I not getting how to turn python
>classes into java classes?
>
>I have the following python class that subclasses from java.util.Random.
>It's a modification of the rand.py code shown in the jython website:
>
>rand.py:
>
>from java.util import Random
>
>class rand(Random):
>    def __init__( self ):
>        "@sig public rand()"
>        Random.__init__( self )
>
>    def nextDouble( self ):
>        return Random.nextDouble( self )
>
>This is turned into a java class with jythonc. It is tested with this
>java file:
>
>TestRand.java:
>
>import rand;
>
>class TestRand
>{
>    public static void main(String args[]){
>        rand firstRand = new rand();
>        System.out.println( firstRand.nextDouble() );
>    }
>}
>
>Executing this java file leads to an "instance already instantiated"
>error. If this sounds familiar to you maybe you've read my previous
>two emails to the list on this problem. Nobody seems to care :-(

Thats wrong; I care, but I am too busy to spend much time on it at the
moment. 

>The code works if you take Random.__init__(self) out of rand.py. But
>this means you cannot call the super class constructor within your own
>init. This sucks! 

Right, and there is *no* way we can fix that. Remember that rand is a
true subclass of Random and there is no way we can execute any jython
(or java) code in the constructor before calling super(). Looking at the
ctor in rand.java the problem is obvious:

    public rand() {
        super();
        __initProxy__(new Object[] {});
    }

The call to __initProxy__ will eventually call rand.__init__ but then
the Random ctor have been called already.

>It must be something I'm doing wrong because the website
>explicitly mentions that you CAN call the super class constructor.

Yes, but that is when the python instance is created before the
proxyinstance. When creating the class from java, the proxyinstance is
create first and then we have to accept the arguments pass from the java
side.

>Please, please, please help me out of my quagmire. I'm dying to use Python
>and if this doesn't work for me I'll be condemned to writing Java code.

Try to change rand.py to (without any @sig for the ctor):

from java.util import Random

class rand(Random):
    def __init__( self):
        pass

    def nextDouble( self ):
        return Random.nextDouble( self )


That will create the two java ctors:

    public rand(long arg0) {
        super(arg0);
        __initProxy__(new Object[] {Py.newInteger(arg0)});
    }

    public rand() {
        super();
        __initProxy__(new Object[] {});
    }

and you can then create an instance of "new rand(42)" from the java test
program. You still can't call the Random.__init__ from python.

I hope this helps.

regards,
finn

[Jython-users] jython with xml

[Michael C. <mc...@de...>]

Hoping someone can help:

I wrote a quick prototype in cpython for my project; but now I'd like to 
compile with jython and run under java. My program uses some things from 
the xml package. At first, I was worried that it wouldn't be possible 
(no parser), but as I was reading xml.sax.__init__.py, I saw that it has 
special casing for the java environment.

1) Can I run something using the xml parser under jython?

2) If so, then what am I doing wrong? I have been setting sys.path to 
include my python 'libs' directory, then importing my package. I get an 
exception:
   File "C:\Applications\Python21\lib\xml\sax\__init__.py", line 88, in 
make_parser
   SAXReaderNotAvailable: No parsers found

This looks bad, but the special-case code must be there for some reason.

Anyone able to help?

-- Michael Chermside

Re: [Jython-users] making packages

[Kevin M. <kev...@er...>]

Hi,

use jythonc -p com.seth.rohit.myPackage A.py

The package can then be found under the 'jpywork' directory

/Kevin

On Tue, 23 Oct 2001, rohit seth wrote:

> Hi,
> I am using jythonc to convert A.py to A.java, A.class.
> I want my corresponding A.class file to be placed
> under some package. How can I do this? That is how can
> I structure my python scripts so that after
> compilation, the corrsponding class files produced are
> part of some package(just like java packages)
> This is required for importing the corresponding class
> files in my java programs.
> Regards,
> Rohit
>
> __________________________________________________
> Do You Yahoo!?
> Make a great connection at Yahoo! Personals.
> http://personals.yahoo.com
>
> _______________________________________________
> Jython-users mailing list
> Jyt...@li...
> https://lists.sourceforge.net/lists/listinfo/jython-users
>

_________________________________________________
Name/Title : Kevin McNamee, Software Consultant
Phone      : +46 13 32 1165

[Jython-users] making packages

[rohit s. <ro2...@ya...>]

Hi,
I am using jythonc to convert A.py to A.java, A.class.
I want my corresponding A.class file to be placed
under some package. How can I do this? That is how can
I structure my python scripts so that after
compilation, the corrsponding class files produced are
part of some package(just like java packages)
This is required for importing the corresponding class
files in my java programs.
Regards,
Rohit

__________________________________________________
Do You Yahoo!?
Make a great connection at Yahoo! Personals.
http://personals.yahoo.com

[Jython-users] Can one call the super class constructor from a Python class init?

[Andres Corrada-E. <co...@ci...>]

Apparently the answer is no if you plan to turn that python class back
into a java class. Is this a bug or am I not getting how to turn python
classes into java classes?

I have the following python class that subclasses from java.util.Random.
It's a modification of the rand.py code shown in the jython website:

rand.py:

from java.util import Random

class rand(Random):
    def __init__( self ):
        "@sig public rand()"
        Random.__init__( self )

    def nextDouble( self ):
        return Random.nextDouble( self )

This is turned into a java class with jythonc. It is tested with this
java file:

TestRand.java:

import rand;

class TestRand
{
    public static void main(String args[]){
        rand firstRand = new rand();
        System.out.println( firstRand.nextDouble() );
    }
}

Executing this java file leads to an "instance already instantiated"
error. If this sounds familiar to you maybe you've read my previous
two emails to the list on this problem. Nobody seems to care :-(

The code works if you take Random.__init__(self) out of rand.py. But
this means you cannot call the super class constructor within your own
init. This sucks! It must be something I'm doing wrong because the website
explicitly mentions that you CAN call the super class constructor.

Please, please, please help me out of my quagmire. I'm dying to use Python
and if this doesn't work for me I'll be condemned to writing Java code.

Andres Corrada-Emmanuel
Senior Research Fellow
Center for Intelligent Information Retrieval
University of Massachusetts, Amherst

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Re: [Jython-users] ImportError: no module named java [YEESH!]

[Ihab A.B. A. <ih...@ah...>]

Hey Robert & everyone,

My sincerest apologies. I was using --

  /opt/jython-2.1a1/

when I should have been using --

  /opt/java/jython-2.1a1/

because, um, well -- the latter, not the former, is where Jython is installed 
on my system!!!! So I fixed my paths and things work now. :)

That said, I think I learned a lot from this experience about setting up the 
Jython environment that I wouldn't have otherwise, so all is well.

Many thanks for all the help. Regards & peace,

Ihab

-- 
Ihab A.B. Awad <ih...@ah...>
Center for Computational Genomics and Bioinformatics,
University of Minnesota. http://www.cbc.umn.edu/~ihab/

Re: [Jython-users] break infinite loop

[<Mat...@i2...>]

Look at Demo/swing/Console.py.  It runs each jython command in its own 
thread, and allows the user to kill that thread by hitting ESC

Matt


On 10/22/2001 01:44:33 PM jython-users-admin wrote:
> 
> somehow tell the interpreter to break out of the current command that
> it is processing and return to the command line so I can preserve as
> much application state as possible.  Any suggestions?

[Jython-users] Error when attempting to create a Proxied object with a constructor

[Max M. <max...@ma...>]

Hi,
	So I've got the PythonInterpreter running inside my Java app  
(thanks to everyone for the pointers to PyServlet example) and I  
successfully get a Proxied class object from this bit of code  that  
looks something like:

         interpreter().execfile(testFile.getAbsolutePath());
	
	PyObject cls = interpreter().get("Test");

          Object o = cls.__tojava__(Class.class);

	Class testClass = (Class)o;

This testClass is the class object for the Test class file read in  
from this Test.py:

from com.webobjects import appserver

class Test(appserver.WOComponent):

	def testName(self):
		"@sig public String testName()"
		return "Hello World"

	So the catch is that a subclass of WOComponent must be  
created with a one argument constructor, soemthing that would  
normally look like Test t = new Test(aWOContext).  So from the  
created Class object I grab the correct constructor and then attempt  
to create the object at which point I get the following exception:

code:
            wocomponent = constructor.newInstance(new Object[] {  
aWOContext });

Exception:

Traceback (innermost last):
  (no code object) at line 0
ImportError: no module named main

Anyone know offhand? Can you create a proxied object via a  
constructor off of the Class object or have I somehow bungled my  
jython environment?  Thanks for any help.

Regards,
	Max







		

Re: [Jython-users] ImportError: no module named java

[Robert W. B. <rb...@di...>]

On Mon, 22 Oct 2001, Ihab A.B. Awad wrote:
> Hi all,
>
> Thanks Robert Bill & Jim Adrig for the tips....
>
> > Yes, os requires the javaos module, and you get the ImportError when that
> > module cannot be Located. Fix= make sure module is found.
>
> I've been trying, in every manner possible! Here's my code --
>
>   rootPath = servletContext.getRealPath("/");
>   if (!rootPath.endsWith(File.separator)) rootPath += File.separator;
>
>   Properties p = getInitParametersAsProperties();
>   p.put(
>     "python.cachedir",
>     servletContext.getAttribute("javax.servlet.context.tempdir").toString());

Maybe try:
    p.put("python.home", "some/path/that/contains/jython's/Lib/dir")

Finding the cachedir will not help jython locate its modules, but finding
the correct python.home will.

>   PythonInterpreter.initialize(System.getProperties(), p, new String[0]);
>
>   PySystemState pySys = Py.getSystemState();
>   pySys.add_classdir(rootPath + "WEB-INF" + File.separator + "classes");
>   pySys.add_extdir(rootPath + "WEB-INF" + File.separator + "lib");
>   pySys.path.append(new PyString(servletContext.getAttribute("python.home") +
>     File.separator + "Lib"));

Maybe try printing python.home to make sure it isn't empty.  Actually,
printing python.home and sys.path is a good test.

>   pySys.path.append(new PyString(rootPath + "WEB-INF" + File.separator +
>    "py"));

Are the jython modules in WEB-INF/py/?  If javaos.py is there, I'm
stumped :(

>   pythonInterpreter = new PythonInterpreter(null, pySys);
>
> I think, based on looking at PyServlet.java, that this should get all my
> bases covered.

Print python.path and python.home to make sure they are correct.  That's
the easiest way to make sure bases are covered.  I would not trust
everything is covered until I got a confirmation that the sys.path
actually did include the directory that javaos.py lives in.

Best of luck.

-robert

> However, I still get --
>
>   import os
>   dir(os)
>
>   Traceback (innermost last): File "", line 10, in ? ImportError: no
>     module named javaos
>
>   import os
>   print os.listdir('/home/ihab')
>
>   Traceback (innermost last): File "", line 2, in ? AttributeError: class
>     'org.python.modules.os' has no attribute 'listdir'
>
> This is all very confusing. Any help appreciated from anyone. Peace,

Re: [Jython-users] ImportError: no module named java

[Ihab A.B. A. <ih...@ah...>]

Hi all,

More re this issue. I finally decided to use PyServlet verbatim, as a 
baseline test case. Here is the relevant part of my "web.xml" file --

  <servlet>
    <servlet-name>PyServlet</servlet-name>
    <servlet-class>org.python.util.PyServlet</servlet-class>
    <init-param>
      <param-name>python.home</param-name>
      <param-value>/opt/java/jython-2.1a1</param-value>
    </init-param>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>PyServlet</servlet-name>
    <url-pattern>*.py</url-pattern>
  </servlet-mapping>

and here is a servlet in Jython --

  from javax.servlet.http import HttpServlet
  import os

  class test(HttpServlet):

    def doGet(self, req, res):
        res.setContentType("text/html");
        out = res.getOutputStream()
        print >>out, "Hello World, how are we?"
        print >>out, dir(os)
        print >>out, os.listdir('/home/ihab')
        out.close()
        return 

Now, when I invoke this, I get the following --

  Hello World, how are we? ['__depends__', 'classDictInit'] 

  A Servlet Exception Has Occurred
    Traceback (innermost last):
    File "/home/ihab/www-docs/logs/../bin/../webapps/omtdb/ ...
      edu/umn/genomics/omtdb/test.py", line 24, in doGet
    AttributeError: class 'org.python.modules.os' has no attribute 'listdir'

so notice that dir(os) does not show any of the symbols that I would expect 
to find and, of course, invoking os.listdir() raises an exception.

Thanks & peace,

Ihab

-- 
Ihab A.B. Awad <ih...@ah...>
Center for Computational Genomics and Bioinformatics,
University of Minnesota. http://www.cbc.umn.edu/~ihab/

Re: [Jython-users] NullPointerException error when calling a python method

[Robert W. B. <rb...@di...>]

Hello Hubert,

On Mon, 22 Oct 2001, yoshizak wrote:
> Hi there,
> I was looking at the error message and the problem with PyProxy lead me 
> to think I should put the jython.jar into the class path (I believe I 
> saw another e-mail in the user archives that said something about this)

Yes, jython.jar is needed.  Using jythonc without the --deep or
--all options compiles your script to java bytecode, but running
that script still requires the Jython classes found in jython.jar.
There are times when using jythonc's --deep and --all options are
beneficial because they allow you to include required jython files
in a single jar.

> don't exactly know why I needed to do this, since I had presumed that 
> this was done by default

Java has no default or intuitive knowledge of Jython, so you
must be explicit about these things when running commands that
start with "java ".

> but when I ran my code sample with
> java -classpath <some directory tree>/jython-2.0/jython.jar:. tryJythonMain
> it finally seemed to run. (Yeah! Finally! :)

Excellent.

> Question is, why did I need to do this? I mean, I'm sure not 'everyone' 
> actually specifies the jar file when running their programs. 

The classes in jython.jar are always needed. Yes, 'everyone'
doesn't always specify the jython.jar file on the command line.
Some have explicitly added it to their classpath by some other
means or they have used jythonc's --deep or --all option.  If you
use --deep/--all, the files from jython.jar are included in the
output jar; but in the end, the files in the jython.jar file are
always needed.

> Do I really 
> need to specify the jar file in the classpath (or CLASSPATH)?

The required classes in jython.jar must get stuck in the classpath
one way or another.


Cheers,
Robert