code: def apply_filters(stream, filters, lexer=None):
      
      def _apply(filter_, stream):
          for token in filter_.filter(lexer, stream):
              yield token
      for filter_ in filters:
          stream = _apply(filter_, stream)
      return stream
docs: Use this method to apply an iterable of filters to
      a stream. If lexer is given it's forwarded to the
      filter, otherwise the filter receives `None`.