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from xml.sax.saxutils import XMLGenerator
from xml.dom import XML_NAMESPACE
from xml.sax.xmlreader import AttributesNSImpl
from rdflib.compat import etree
from rdflib import Literal, URIRef, BNode, Graph, Variable
from rdflib.query import (
Result,
ResultParser,
ResultSerializer,
ResultException
)
SPARQL_XML_NAMESPACE = u'http://www.w3.org/2005/sparql-results#'
RESULTS_NS_ET = '{%s}' % SPARQL_XML_NAMESPACE
"""A Parser for SPARQL results in XML:
http://www.w3.org/TR/rdf-sparql-XMLres/
Bits and pieces borrowed from:
http://projects.bigasterisk.com/sparqlhttp/
Authors: Drew Perttula, Gunnar Aastrand Grimnes
"""
class XMLResultParser(ResultParser):
def parse(self, source):
return XMLResult(source)
class XMLResult(Result):
def __init__(self, source):
xmlstring = source.read()
if isinstance(xmlstring, unicode):
xmlstring = xmlstring.encode('utf-8')
try:
tree = etree.fromstring(xmlstring)
except Exception, e:
try:
raise e.__class__("error parsing %r: %s" % (xmlstring, e))
except:
raise e
boolean = tree.find(RESULTS_NS_ET + 'boolean')
results = tree.find(RESULTS_NS_ET + 'results')
if boolean is not None:
type_ = 'ASK'
elif results is not None:
type_ = 'SELECT'
else:
g = Graph()
try:
g.parse(data=xmlstring)
if len(g) == 0:
raise
type_ = 'CONSTRUCT'
except:
raise ResultException(
"No RDF Graph, result-bindings or boolean answer found!")
Result.__init__(self, type_)
if type_ == 'SELECT':
self.bindings = []
for result in results:
r = {}
for binding in result:
r[Variable(binding.get('name'))] = parseTerm(binding[0])
self.bindings.append(r)
self.vars = [Variable(x.get("name"))
for x in tree.findall(
'./%shead/%svariable' % (
RESULTS_NS_ET, RESULTS_NS_ET))]
elif type_ == 'ASK':
self.askAnswer = boolean.text.lower().strip() == "true"
elif type_ == 'CONSTRUCT':
self.graph = g
def parseTerm(element):
"""rdflib object (Literal, URIRef, BNode) for the given
elementtree element"""
tag, text = element.tag, element.text
if tag == RESULTS_NS_ET + 'literal':
if text is None:
text = ''
datatype = None
lang = None
if element.get('datatype', None):
datatype = URIRef(element.get('datatype'))
elif element.get("{%s}lang" % XML_NAMESPACE, None):
lang = element.get("{%s}lang" % XML_NAMESPACE)
ret = Literal(text, datatype=datatype, lang=lang)
return ret
elif tag == RESULTS_NS_ET + 'uri':
return URIRef(text)
elif tag == RESULTS_NS_ET + 'bnode':
return BNode(text)
else:
raise TypeError("unknown binding type %r" % element)
class XMLResultSerializer(ResultSerializer):
def __init__(self, result):
ResultSerializer.__init__(self, result)
def serialize(self, stream, encoding="utf-8"):
writer = SPARQLXMLWriter(stream, encoding)
if self.result.type == 'ASK':
writer.write_header([])
writer.write_ask(self.result.askAnswer)
else:
writer.write_header(self.result.vars)
writer.write_results_header()
for b in self.result.bindings:
writer.write_start_result()
for key, val in b.iteritems():
writer.write_binding(key, val)
writer.write_end_result()
writer.close()
# TODO: Rewrite with ElementTree?
class SPARQLXMLWriter:
"""
Python saxutils-based SPARQL XML Writer
"""
def __init__(self, output, encoding='utf-8'):
writer = XMLGenerator(output, encoding)
writer.startDocument()
writer.startPrefixMapping(u'', SPARQL_XML_NAMESPACE)
writer.startPrefixMapping(u'xml', XML_NAMESPACE)
writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'sparql'),
u'sparql', AttributesNSImpl({}, {}))
self.writer = writer
self._output = output
self._encoding = encoding
self._results = False
def write_header(self, allvarsL):
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'head'),
u'head', AttributesNSImpl({}, {}))
for i in xrange(0, len(allvarsL)):
attr_vals = {
(None, u'name'): unicode(allvarsL[i]),
}
attr_qnames = {
(None, u'name'): u'name',
}
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'variable'),
u'variable', AttributesNSImpl(attr_vals, attr_qnames))
self.writer.endElementNS((SPARQL_XML_NAMESPACE,
u'variable'), u'variable')
self.writer.endElementNS((SPARQL_XML_NAMESPACE, u'head'), u'head')
def write_ask(self, val):
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'boolean'),
u'boolean', AttributesNSImpl({}, {}))
self.writer.characters(str(val).lower())
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'boolean'), u'boolean')
def write_results_header(self):
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'results'),
u'results', AttributesNSImpl({}, {}))
self._results = True
def write_start_result(self):
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'result'),
u'result', AttributesNSImpl({}, {}))
self._resultStarted = True
def write_end_result(self):
assert self._resultStarted
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'result'), u'result')
self._resultStarted = False
def write_binding(self, name, val):
assert self._resultStarted
attr_vals = {
(None, u'name'): unicode(name),
}
attr_qnames = {
(None, u'name'): u'name',
}
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'binding'),
u'binding', AttributesNSImpl(attr_vals, attr_qnames))
if isinstance(val, URIRef):
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'uri'),
u'uri', AttributesNSImpl({}, {}))
self.writer.characters(val)
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'uri'), u'uri')
elif isinstance(val, BNode):
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'bnode'),
u'bnode', AttributesNSImpl({}, {}))
self.writer.characters(val)
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'bnode'), u'bnode')
elif isinstance(val, Literal):
attr_vals = {}
attr_qnames = {}
if val.language:
attr_vals[(XML_NAMESPACE, u'lang')] = val.language
attr_qnames[(XML_NAMESPACE, u'lang')] = u"xml:lang"
elif val.datatype:
attr_vals[(None, u'datatype')] = val.datatype
attr_qnames[(None, u'datatype')] = u'datatype'
self.writer.startElementNS(
(SPARQL_XML_NAMESPACE, u'literal'),
u'literal', AttributesNSImpl(attr_vals, attr_qnames))
self.writer.characters(val)
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'literal'), u'literal')
else:
raise Exception("Unsupported RDF term: %s" % val)
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'binding'), u'binding')
def close(self):
if self._results:
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'results'), u'results')
self.writer.endElementNS(
(SPARQL_XML_NAMESPACE, u'sparql'), u'sparql')
self.writer.endDocument()
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