code: def _blobs_page_start(iterator, page, response):
      
      page.prefixes = tuple(response.get("prefixes", ()))
      iterator.prefixes.update(page.prefixes)
docs: Grab prefixes after a :class:`~google.cloud.iterator.Page` started.
  
      :type iterator: :class:`~google.api_core.page_iterator.Iterator`
      :param iterator: The iterator that is currently in use.
  
      :type page: :class:`~google.cloud.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 blobs.