Re: [Jython-users] Package attributes not reachable from Python-derivedJava classes

[Kevin B. <kb...@ca...>]

You can do it just fine, but you have to set 'respectJavaAccessibility=false' in the jython registry (and this requires some permission in the Java VM - usually not a problem for Java applications, but applets may have problems).

The reason that you still need to set this flag, even though you are generating code in the appropriate package  , is that jythonc generates java code that uses the Python interpreter classes to do the method/attribute lookup. This means that the Python classes are trying to access the protected attribute, rather than the class that you generated.

Example from my generated code, attempting to access the '_package' variable (package protected):

           Py.printComma(frame.getlocal(0).__getattr__("_package"));

Note that it isn't doing the reflection itself, but is delegating to PyObject to do the reflection.

My code & makefile attached below.

kb

---Attribute.java
package test;

public class Attribute
{
    private int _private = 1;
    int _package = 2;
    protected int _protected = 3;
    public int _public = 4;
}


---testAttribute.py
from test import Attribute
class X( Attribute ):
    def go( self ):
    	print self._package, self._private, self._protected, self._public

X().go()

---Makefile
testAttribute:
	javac -d . Attribute.java
	jythonc --package test testAttribute.py
	java -classpath .\;./jpywork\;w:/tools/jython/jython.jar test.testAttribute

---command:
make testAttribute

---output:
javac -d . Attribute.java
jythonc --package test testAttribute.py
processing testAttribute

Required packages:
  test

Creating adapters:

Creating .java files:
  testAttribute module
    X extends test.Attribute

Compiling .java to .class...
Compiling with args: ['D:\\jdk1.3\\bin\\javac', '-classpath', '"w:/tools/jython/jython.jar;.;w:\\classes;w:\\lib\\ldapjdk.jar;w:\\lib\\xerces.jar;w:\\lib\\ldap.jar;w:\\lib\\providerutil.jar;w:\\lib\\jaas.jar;w:\\lib\\jndi.jar;w:\\lib\\ldapbp.jar;w:\\lib\\jsse-export\\jnet.jar;w:\\lib\\jsse-export\\jsse.jar;w:\\jars\\servlet.jar;w:\\;.\\jpywork;;w:\\tools\\jython\\Tools\\jythonc;e:\\work\\kb\\test\\jython\\.;w:\\tools\\jython\\Lib;w:\\src\\com\\pipeline\\test\\bom;w:\\src\\com\\pipeline\\test;d:\\python;w:\\tools\\jython"', '.\\jpywork\\test\\testAttribute.java']
0  Note: Some input files use or override a deprecated API.
Note: Recompile with -deprecation for details.

java -classpath .\;./jpywork\;w:/tools/jython/jython.jar test.testAttribute
2 1 3 4


The '2 1 3 4' is the output of the command.

It looks like it works to me - note that I have 'respectJavaAccessibility=false' in my jython registry.

If I have 'respect...=true', I get:

Java Traceback:

	at org.python.core.Py.AttributeError(Py.java:90)
	at org.python.core.PyObject.__getattr__(PyObject.java:692)
	at test.testAttribute$_PyInner.go$1(testAttribute.java:43)
	at test.testAttribute$_PyInner.call_function(testAttribute.java:32)
	at org.python.core.PyTableCode.call(PyTableCode.java:198)
	at org.python.core.PyTableCode.call(PyTableCode.java:253)
	at org.python.core.PyFunction.__call__(PyFunction.java:170)
	at org.python.core.PyInstance.invoke(PyInstance.java:236)
	at test.testAttribute$_PyInner.main$3(testAttribute.java:59)
	at test.testAttribute$_PyInner.call_function(testAttribute.java:36)
	at org.python.core.PyTableCode.call(PyTableCode.java:198)
	at org.python.core.PyCode.call(PyCode.java:13)
	at org.python.core.imp.createFromCode(imp.java:165)
	at org.python.core.Py.runMain(Py.java:818)
	at test.testAttribute.main(testAttribute.java:110)
Traceback (innermost last):
  File "E:\work\kb\test\jython\testAttribute.py", line 0, in main
  File "E:\work\kb\test\jython\testAttribute.py", line 0, in go
AttributeError: instance of 'X' has no attribute '_package'

kb

Andres Corrada-Emmanuel wrote:
> 
> 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
> 
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