code: def _rows_page_start(iterator, page, response):
      
      total_rows = response.get("totalRows")
      if total_rows is not None:
          total_rows = int(total_rows)
      iterator._total_rows = total_rows
docs: Grab total rows when :class:`~google.cloud.iterator.Page` starts.
  
      :type iterator: :class:`~google.api_core.page_iterator.Iterator`
      :param iterator: The iterator that is currently in use.
  
      :type page: :class:`~google.api_core.page_iterator.Page`
      :param page: The page that was just created.
  
      :type response: dict
      :param response: The JSON API response for a page of rows in a table.