docs: def print_sub(tables):
      """Dummy print sub.
  
      :param tables: print events of tables.
      """
      logger = logging.getLogger("meepo.sub.print_sub")
      logger.info("print_sub tables: %s" % ", ".join(tables))
  
      if not isinstance(tables, (list, set)):
          raise ValueError("tables should be list or set")
  
      events = ("%s_%s" % (tb, action) for tb, action in
                itertools.product(*[tables, ["write", "update", "delete"]]))
      for event in events:
          signal(event).connect(
              lambda pk: logger.info("%s -> %s" % event, pk), weak=False)