code: def request_roster(self, version = None):
          
          processor = self.stanza_processor
          request = Iq(stanza_type = "get")
          request.set_payload(RosterPayload(version = version))
          processor.set_response_handlers(request,
                                      self._get_success, self._get_error)
          processor.send(request)
docs: Request roster from server.
  
          :Parameters:
              - `version`: if not `None` versioned roster will be requested
                for given local version. Use "" to request full roster.
          :Types:
              - `version`: `unicode`