code: def ws_url(server: Server, prefix: str = "") -> str:
      return f"ws://localhost:{server.port}{prefix}/ws"
  
imports: from __future__ import annotations
  import logging
  from typing import TYPE_CHECKING, Any
  from tornado.httpclient import AsyncHTTPClient, HTTPRequest
  from tornado.websocket import WebSocketClientConnection, websocket_connect
label_desc: Use image node_id 2 for calling a global function with example usage: ws_url(server, prefix) and returns: str, server, prefix, str