code: def rdf_iterator(graph, lang, add_vtype=False):
      
      # Return the header row
      hdr = ('subject', 'predicate', 'object')
      yield hdr if not add_vtype else ((h, 'type') for h in hdr)
      # Now the data rows
      for row in graph:
          if lang and not lang_match_rdf(row, lang):
              continue
          yield ((unicode(c), gtype(c)) for c in row)
docs: Convert a Graph response into a double iterable, by triples and elements.
      Optionally add element type, and filter triples by language (on literals)