code: def _getPrefixURL(self, url):
          
          for prefix, namespace in self._rdfGraph.namespaces():
              if namespace.toPython() in url:
                  return namespace
docs: Given a url return namespace prefix.
          Leverages prefixes already in graph namespace
          Ex.  "http://www.drugbank.ca/drugs/DDD"
              -> "http://www.drugbank.ca/drugs/"