code: def mark_notifications(self, last_read=''):
          
          url = self._build_url('notifications', base_url=self._api)
          mark = {'read': True}
          if last_read:
              mark['last_read_at'] = last_read
          return self._boolean(self._put(url, data=dumps(mark)),
                               205, 404)
docs: Mark all notifications in this repository as read.
  
          :param str last_read: (optional), Describes the last point that
              notifications were checked. Anything updated since this time will
              not be updated. Default: Now. Expected in ISO 8601 format:
              ``YYYY-MM-DDTHH:MM:SSZ``. Example: "2012-10-09T23:39:01Z".
          :returns: bool