code: def blacklist(self, host):
      if not self._hosts_state[host].is_blacklisted():
          logging.info("blacklist failing host: {}".format(host))
      self._hosts_state[host].blacklist()
  
imports: import io
  import logging
  import random
  import threading
  import time
  from collections import defaultdict
  from horovod.runner.common.util import safe_shell_exec
  from horovod.runner.elastic.worker import HostUpdateResult
label_desc: Use image node_id 4 for calling the HostManager obj's underlying member method code with example usage: obj.blacklist(host) without return types