Exception with SPARQL rdflib property paths

Question

I have the following SPARQL query:

SELECT ?s ?p ?o
WHERE {
?sbj ?p ?obj .
?sbj (<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>/<http://www.w3.org/2000/01/rdf-schema#subClassOf>+) <http://www.my.org/ontology.owl#Place> .
?sbj rdfs:label ?s .
?obj rdfs:label ?o .
}

Which make use of the Property Paths defined for SPARQL 1.1.

I'm trying to process this query with rdflib 3.4.0 and I receive the following exception message:

rayman@hal9100 ~/projects/scripts $ python places_owl2json.py 
Traceback (most recent call last):
  File "places_owl2json.py", line 107, in <module>
    """)
  File "/usr/local/lib/python2.7/dist-packages/rdflib/graph.py", line 1007, in query
    query_object, initBindings, initNs, **kwargs))
  File "/usr/local/lib/python2.7/dist-packages/rdfextras/sparql/processor.py", line 49, in query
    loadContexts=loadContexts)
  File "/usr/local/lib/python2.7/dist-packages/rdfextras/sparql/algebra.py", line 406, in TopEvaluate
    assert isinstance(expr,AlgebraExpression), repr(expr)
AssertionError: None

What's the problem? Thanks,

Riccardo

Answer 1

this seems to have been a bug in rdflib 3.4.0: i tried reproducing the error on rdflib 4.2.1-dev (current version) and it seems to work with the code below:

In [1]: from rdflib import *
INFO:rdflib:RDFLib Version: 4.2.1-dev

In [2]: g = Graph()

In [3]: g.query('''
   ...: SELECT ?s ?p ?o
   ...: WHERE {
   ...: ?sbj ?p ?obj .
   ...: ?sbj (<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>/<http://www.w3.org/2000/01/rdf-schema#subClassOf>+) <http://www.my.org/ontology.owl#Place> .
   ...: ?sbj rdfs:label ?s .
   ...: ?obj rdfs:label ?o .
   ...: }
   ...: ''')
Out[3]: <rdflib.plugins.sparql.processor.SPARQLResult at 0x1111dc410>