[redland-dev] failure in librdf_new_node_from_typed_literal (was: Re: newbie question: constructing a literal with datatype using Python bindings)

[Sean Boisen]

Sean Boisen <sean at ...> writes:
> 
> I'm trying to construct a literal URI with datatype, e.g. something (in
> N-triples) like
> "true"^^<http://www.w3.org/2001/XMLSchema#boolean>
> The documentation is a bit terse on this point. I'm new to Redland, so
> please be gentle.
> 
> Here's what I tried that _didn't_ work (parading my ignorance):
> # string argument to datatype as URI
> >>> rdfalse = RDF.Node(literal="false",
> datatype="http://www.w3.org/2001/XMLSchema#boolean")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
>   File "C:\Python24\Lib\site-packages\RDF\RDF.py", line 302, in __init__
>     args['literal'], xml_language, datatype._reduri)
> AttributeError: 'str' object has no attribute '_reduri'
> 
> # Uri argument
> >>> rdfalse = RDF.Node(literal="false",
> datatype=RDF.Uri("http://www.w3.org/2001/XMLSchema#boolean"))
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
>   File "C:\Python24\Lib\site-packages\RDF\RDF.py", line 322, in __init__
>     raise RedlandError("Node construction failed")
> RDF.RDF.RedlandError: 'Node construction failed'
> 
> # maybe the datatype argument needs to be a Node with a URI?
> >>> xsdbool =
> RDF.Node(RDF.Uri("http://www.w3.org/2001/XMLSchema#boolean"))
> >>> rdfalse = RDF.Node(literal="false", datatype=xsdbool)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
>   File "C:\Python24\Lib\site-packages\RDF\RDF.py", line 302, in __init__
>     args['literal'], xml_language, datatype._reduri)
> AttributeError: 'Node' object has no attribute '_reduri'
> 
> # datatype arg as a literal Node?
> >>> xsdbool =
> RDF.Node(literal="http://www.w3.org/2001/XMLSchema#boolean")
> >>> xsdbool.is_literal()
> True
> >>> rdfalse = RDF.Node(literal="false", datatype=xsdbool)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
>   File "C:\Python24\Lib\site-packages\RDF\RDF.py", line 302, in __init__
>     args['literal'], xml_language, datatype._reduri)
> AttributeError: 'Node' object has no attribute '_reduri'
> 
> I've pawed around in the code a bit but not enough to really understand
> where this is going wrong, and I'm assuming it's something simple about
> the conceptual model that I just don't have right yet. 
> 
> This is on Windows Vista, Python 2.4, using the binaries and installer
> from http://download.librdf.org/binaries/win32/1.0.3/, RDF.py,v 1.116
> 2006-03-05 08:30:38 (in the unlikely event that matters). 
> 
> Sean
> 

I've looked into the details a bit further, and either there's a bug lurking
here, or i'm really not getting it.

In the Python bindings, it looks like the right invocation should be:

>>> rdfalse = RDF.Node(literal="false",
datatype=RDF.Uri("http://www.w3.org/2001/XMLSchema#boolean"))

(because the argument to datatype has to have a _reduri property). 

As evidenced below, this raises the "Node construction failed" error, because
the call to 

self._node=Redland.librdf_new_node_from_typed_literal(_world._world,
          args['literal'], xml_language, datatype._reduri)

returns None. That's as far as i'm able to penetrate, though, since i'm using
the binaries from http://download.librdf.org/binaries/win32/1.0.3/ (which looks
a couple of revs behind, but i don't have the proper kit to build more current
windows binaries: if somebody knows of one, please let me know and i'll give it
a try). 

This example from the documentation similarly fails:

node5=RDF.Node(literal="<tag>content</tag>", is_wf_xml=1)

which makes me think there's something wrong with the binaries. 

Can anybody shed some light on this? Do these forms work for others using Python?

Sean