code: def filter(self, result):
          
          if result is None:
              return True
          reject = result in self.history
          if reject:
              log.debug('result %s, rejected by\n%s', Repr(result), self)
          return reject
docs: Filter the specified result based on query criteria.
          @param result: A potential result.
          @type result: L{sxbase.SchemaObject}
          @return: True if result should be excluded.
          @rtype: boolean