code: def mark_all(request):
      
      action = request.POST.get('action', None)
      success = True
  
      if action == 'read':
          request.user.notifications.read_all()
          msg = _("Marked all notifications as read")
      elif action == 'unread':
          request.user.notifications.unread_all()
          msg = _("Marked all notifications as unread")
      else:
          msg = _("Invalid mark action")
          success = False
  
      ctx = {'msg': msg, 'success': success, 'action': action}
  
      return notification_redirect(request, ctx)
docs: Marks notifications as either read or unread depending of POST parameters.
      Takes ``action`` as POST data, it can either be ``read`` or ``unread``.
  
      :param request: HTTP Request context.
  
      :return: Response to mark_all action.