code: def update_universe(id_or_symbols):
      
      if isinstance(id_or_symbols, (six.string_types, Instrument)):
          id_or_symbols = [id_or_symbols]
      order_book_ids = set(
          assure_order_book_id(order_book_id) for order_book_id in id_or_symbols
      )
      if order_book_ids != Environment.get_instance().get_universe():
          Environment.get_instance().update_universe(order_book_ids)
docs: 该方法用于更新现在关注的证券的集合（e.g.：股票池）。PS：会在下一个bar事件触发时候产生（新的关注的股票池更新）效果。并且update_universe会是覆盖（overwrite）的操作而不是在已有的股票池的基础上进行增量添加。比如已有的股票池为['000001.XSHE', '000024.XSHE']然后调用了update_universe(['000030.XSHE'])之后，股票池就会变成000030.XSHE一个股票了，随后的数据更新也只会跟踪000030.XSHE这一个股票了。
  
      :param id_or_symbols: 标的物
      :type id_or_symbols: :class:`~Instrument` object | `str` | List[:class:`~Instrument`] | List[`str`]