Trying to replace SPARQL query using RDFAlchemy's rdfSubject

rdfalchemy_test_dbpedia2.py

"""
See RDFAlchemy-dev list discussion:

https://groups.google.com/forum/?hl=en&fromgroups=#!topic/rdfalchemy-dev/D1AyXQwmOuw

"""


from rdfalchemy import rdfSingle, rdfSubject
from rdfalchemy.sparql import SPARQLGraph
from rdflib import Namespace

query = """
PREFIX db: <http://dbpedia.org/resource/>
PREFIX dbprop: <http://dbpedia.org/property/>
PREFIX dbonto: <http://dbpedia.org/ontology/>

SELECT distinct ?name ?label {
    ?artist
        a dbonto:MusicalArtist;
        dbprop:birthName ?name.
    {
        ?artist dbonto:instrument db:Guitar .
        db:Guitar rdfs:label ?label.
    }
    UNION
    {
    ?artist  dbonto:instrument db:Piano .
    db:Piano rdfs:label ?label .
    }
    FILTER ( lang(?name) = "en" )
}
ORDER BY ?name
LIMIT 10
"""

DB = Namespace('http://dbpedia.org/resource/')
DBPROP = Namespace('http://dbpedia.org/property/')
DBONTO = Namespace('http://dbpedia.org/ontology/')
RDFS = Namespace('http://www.w3.org/2000/01/rdf-schema#')

endpoint = "http://live.dbpedia.org/sparql"
graph = SPARQLGraph(endpoint)

rdfSubject.db = graph

class Instrument(rdfSubject):
    rdfs_label = rdfSingle(RDFS.label, 'label')

class MusicalArtist(rdfSubject):
    rdf_type = DBONTO.MusicalArtist
    dbprop_birthname = DBPROP.birthName
    dbonto_instrument = Instrument  # ?

guitar_players = MusicalArtist.get_by(dbonto_instrument=DB.Guitar)
# Line above throws "AttributeError: type object 'rdfSubject' has no attribute 'pred'"