[Jython-users] jythonc can't return Python object

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

dman's jythonc use brought up an interesting limitation in jythonc:

A java-object method cannot return an instance of a java-object subclass created by jythonc.

For example, in the following code, a method on 'ep' can't return an instance of 'ep' (the same failure occurs if the 'returned value' and the class-returning the value are separate classes in separate files.)

--- ep.py
import java
class ep( java.lang.Object ):
    def go( self ):
        """@sig public ep go()"""
        return None
    

jythonc complains that it cannot find the 'ep' class:

cd e:/work/kb/jythonc/extendPython/
jythonc ep.py
processing ep

Required packages:
  java.lang

Creating adapters:

Creating .java files:
  ep module
Traceback (innermost last):
  File "w:/tools/jython\Tools\jythonc\jythonc.py", line 5, in ?
  File "w:\tools\jython\Tools\jythonc\main.py", line 300, in main
  File "w:\tools\jython\Tools\jythonc\main.py", line 221, in doCompile
  File "w:\tools\jython\Tools\jythonc\compile.py", line 381, in dump
  File "w:\tools\jython\Tools\jythonc\compile.py", line 318, in processModule
  File "w:\tools\jython\Tools\jythonc\compile.py", line 147, in makeJavaProxy
  File "w:\tools\jython\Tools\jythonc\compile.py", line 53, in getsig
  File "w:\tools\jython\Tools\jythonc\compile.py", line 84, in insistJavaClass
ValueError: can not find class: ep

The reason this fails is that compile.py insists that any Java classes exist (presumably to prevent you from trying to return a Python object that isn't a java subclass - the generated Java code would fail in that case.) Because the generated code hasn't been compiled w/ javac yet, compile.py can't find the Java class, and throws the ValueError.

Is this a bug, a quirk, or "a bug but we're not about to fix it"?

:-)

kb

    


dman wrote:
> 
> On Fri, Nov 02, 2001 at 03:50:12PM +0000, Finn Bock wrote:
> | [dman]
> |
> | >I'm trying to use Jython(c) to allow using Moshe Zadka's PMS framework
> | >along with a Java/Swing GUI for a school project.  (The other group
> | >members are writing the gui and they don't know python)  I've run into
> | >a couple of problems, though, all related to java's type system.
> | >
> | >There are several modules in the PMS package.  I have taken the base
> | >classes of the inheritance tree and made them inherit from
> | >java.lang.Object and added the @sig lines.  A simplified example :
> | >
> | >----- PMS/AbstractFolder.py
> | >class AbstractFolder( java.lang.Object ) : pass
> | >
> | >----- PMS/Folder.py
> | >import AbstractFolder
> | >class Folder( AbstractFolder.AbstractFolder ) : pass
> | >
> | >
> | >I also have the following class as a factory for the GUI to create a
> | >hardcoded folder for the prototype demo.
> | >
> | >----- DemoFolder1.py
> | >class DemoFolder1( java.lang.Object ) :
> | >    def make( self , name ) :
> | >        """
> | >        @sig public Object make( String name )
> | >        """
> | >
> | >        server = PMS.MaildirServer.MaildirServer( "server_name" , "." )
> | >        PMS.Configuration.Configuration().servers[ server ] = lambda x : x
> | >        folder = PMS.Folder.Folder( server , name )
> | >        folder.create()
> | >
> | >        print folder.__class__ # correctly prints "PMS.Folder.Folder"
> | >        return folder
> | >
> | >
> | >
> | >I used jythonc to compile the stuff, and everything compiles fine.
> | >The Java code that uses this looks like :
> | >
> | >
> | >            Object folder = (new DemoFolder1()).make( "Demo1" );
> | >            MailMessage.Message message = new MailMessage.Message();
> | >
> | >            // This line prints out
> | >            // org.python.proxies.PMS.Folder$Folder$2
> | >            System.out.println( folder.getClass() ) ;
> |
> | The strange classname comes from the dynamic proxy generation.
> 
> Yeah, the name is nicely self-documenting :-).
> 
> | Verify if jythonc created a java class for the Folder class. You
> | check that in the stdout from jythonc where there should be a line
> | like:
> |
> |  Folder extends java.lang.Object
> |
> | If no such line is written, it is because jythonc failed to detect
> | that Folder is a java subclass.
> 
> What I see is :
> 
>   AbstractFolder module
>       AbstractFolder extends java.lang.Object
>       NoSuchMessageError extends java.lang.Exception
>   Folder module
>       Folder extends AbstractFolder
> 
> So Folder is indirectly a java subclass.
> 
> I had originally tried
> 
>     class Folder( java.lang.Object , AbstractFolder.AbstractFolder ) : pass
> 
> but jythonc raises :
> 
>     TypeError: no multiple inheritance for Java classes: org.python.proxies.AbstractFolder$AbstractFolder$6 and java.lang.Object
> 
> Kevin Butler wrote to me off-list and mentioned trying the __tojava__
> stuff.  This fails because I can't cast the above class to PyObject.
> If I change the @sig to return PyObject, then the __tojava__ call
> succeeds, but gives me a PySingleton instance, not a Folder instance.
> 
> Is there a solution other than creating a python class to provide
> pseudo-reflection to java?  (it takes a java.lang.Object and a name
> and invokes it in python ; this works but isn't natural from the java
> side)
> 
> Thanks for your response!
> 
> -D
> 
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