code: def _ray_pretask(self, key, object_refs):
      self.pb.task_scheduled.remote(key, datetime.now())
  
imports: import contextlib
  from collections import namedtuple, defaultdict
  from datetime import datetime
  from dask.callbacks import Callback
label_desc: Use image node_id 3 for calling the ProgressBarCallback obj's underlying member method code with example usage: obj._ray_pretask(key, object_refs) without return types