RE: [Jython-dev] Py.java2py

[brian z. <bz...@zi...>]

Thanks for the input on checking sequences.  That's precisely the type of
information I was looking forward.  Is there any place where best practices
are written down?

I'll keep in mind your comments for the Python wrapper factory.  I like that
latter as well.

thanks,

brian

> -----Original Message-----
> From: jyt...@li...
> [mailto:jyt...@li...]On Behalf Of Finn Bock
> Sent: Wednesday, February 28, 2001 7:15 AM
> To: jyt...@li...
> Subject: Re: [Jython-dev] Py.java2py
>
>
> On Tue, 27 Feb 2001 07:30:57 -0600, you wrote:
>
> >The reason I ask is I have some code which wants to iterate an instance
> >using __len__ and __finditem__ magic methods on any sequence.
>
> Incidently, I hope you are aware that __len__ are allowed to lie. The
> only correct way to iterate over a sequence from java are:
>
>   PyObject item;
>   for (int i = 0; (item = seq.__finditem__(i)) != null; i++)
>     ;
>
> >I'll accept
> >anything with those two methods and I thought the Collection
> classes where
> >wrapped as such (thus my previous question about CollectionProxy; after
> >thinking about, it makes sense as to why Java classes come in as
> >PyJavaInstance instances.).  In the meantime I do this:
> >
> >protected boolean isSeq(PyObject object) {
> >	if(object instanceof PyJavaInstance) {
> >		List list = (List)object.__tojava__(List.class);
> >		if(list == Py.NoConversion) {
> >			return false;
> >		}
> >		object = new PyList((PyObject[])list.toArray(new
> PyObject[list.size()]));
> >	}
> >	return object.__findattr__("__finditem__") != null &&
> >object.__findattr__("__len__") != null;
> >}
>
> It should probably use __findattr__("__getitem__") if you want it to
> succeed on python classes with a "def __getitem__(self,idx):" method.
>
> OTOH, the best way of testing an objects sequence-ness is by indexing
> it:
>
>    protected boolean isSeq(PyObject object) {
>        try {
>            object.__finditem__(0);
>        } catch (PyException exc) {
>            return !Py.matchException(exc, Py.AttributeError);
>        }
>        return true;
>    }
>
> Generally the python language is very weak in this array. Jython's
> addition of java object does not improve the situation at all.
>
> >I'll look into writing the Java->Python wrapper factory and the
> developers
> >can do what they want with it.
> >
> >As for subclass support, would not Class.isAssignableFrom(Class) be
> >sufficient for handling these cases.    I'm thinking of this off
> the top of
> >my head so I'll have to test it out first.
>
> Indeed that would work.
>
> Implementation wise I can come up with two simple design. One use a
> hashtable where the subclass support is difficult to achive, the other
> use a list of two-tuples that is traversed sequentually where it is
> easy. I think the list is best, but only if it can be self-sorting:
>
> If a user add one wrapper for java.util.Vector and another for
> java.util.List, the Vector must be tested before the List in the list. I
> don't want the user to be concerned about this sequence.
>
> regards,
> finn
>
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