code: def filter_by_db_refs(stmts_in, namespace, values, policy, **kwargs):
      invert = kwargs.get('invert', False)
      match_suffix = kwargs.get('match_suffix', False)
      if policy not in ('one', 'all'):
          logger.error('Policy %s is invalid, not applying filter.' % policy)
          return
      else:
          name_str = ', '.join(values)
          rev_mod = 'not ' if invert else ''
          logger.info(('Filtering %d statements for those with %s agents %s'
                       'grounded to: %s in the %s namespace...') %
                          (len(stmts_in), policy, rev_mod, name_str, namespace))
      def meets_criterion(agent):
          if namespace not in agent.db_refs:
              return False
          entry = agent.db_refs[namespace]
          if isinstance(entry, list):
              entry = entry[0][0]
          ret = False
          if match_suffix:
              if any([entry.endswith(e) for e in values]):
                  ret = True
          else:
              if entry in values:
                  ret = True
          if invert:
              return not ret
          else:
              return ret
      enough = all if policy == 'all' else any
      stmts_out = [s for s in stmts_in
                   if enough([meets_criterion(ag) for ag in s.agent_list()
                              if ag is not None])]
      logger.info('%d Statements after filter...' % len(stmts_out))
      dump_pkl = kwargs.get('save')
      if dump_pkl:
          dump_statements(stmts_out, dump_pkl)
      return stmts_out