code: def keep_alive(self) -> None:
      assert self.sock, "must be started first"
      self.sock.send(b"k")
  
imports: import logging
  import os
  import selectors
  import signal
  import socket
  import subprocess
  import time
  from typing import Any, Callable, Dict, List, Optional, Tuple, Union
  import determined
label_desc: Use image node_id 6 for calling the PIDClient obj's underlying member method code with example usage: obj.keep_alive() without return types