converts a result's bindings to their corresponding rdflib terms, e.g. URIref, Literal, BNode

sparqlwrapperResToRDFlib.py

# -*- coding: utf-8 -*-
'''
Created on Oct 30, 2010

@author: joern
'''
import rdflib

def sparqlJSONresultBindingsToRDFlib(resBindings):
    """ Converts a result's bindings as retrieved in res["results"]["bindings"]
        by SPARQLWrapper with a sparql select query into the corresponding
        list with rdflib terms, e.g., Literal, URIref, BNode.
        BNodes won't be mixed between iterated calls of this function even if
        they happen to have the same "value". Internally the given value is mapped
        to a random value, which is remembered in _one and the same_ call of this
        function only."""
    
    _bnodes = {} # makes sure we don't confuse BNodes from different results
    
    def dictToRDFlib(d):
        """ Maps a dict following the syntax in http://www.w3.org/TR/rdf-sparql-json-res/
            to the corresponding rdflib term. """
        
        if d == None: return None
        
        t = d["type"]
        v = d["value"]
        
        if t == "uri":
            return rdflib.URIRef(v)
        
        if t == "bnode":
            if v not in _bnodes:
                _bnodes[v] = rdflib.BNode() # v is not used as BNode value on purpose (multiple calls should not have the same value)
            return _bnodes[v]
        
        l = d.get("xml:lang", None)
        if t == "literal":
            return rdflib.Literal(v, lang=l)
        
        if t == "typed-literal":
            return rdflib.Literal(v, lang=l, datatype=d["datatype"]) # will raise type error if lang and datatype set
        
        raise rdflib.exceptions.ParserError(
            "Invalid sparql json result according to http://www.w3.org/TR/rdf-sparql-json-res/: {0}".format(d))
    
    resBindingsRDFlib = []
    for row in resBindings:
        tmp = {}
        for k,v in row.items():
            tmp[k] = dictToRDFlib(v)
        resBindingsRDFlib.append(tmp)
    
    return resBindingsRDFlib