code: def apply(self, fn):
      return fn(self)
  
file_path: ray/rllib/tests/mock_worker.py
imports: import numpy
  import ray
  from ray.rllib.evaluation.worker_set import WorkerSet
  from ray.rllib.policy.sample_batch import SampleBatch
  from ray.rllib.utils.filter import MeanStdFilter
label_desc: Use image node_id 9 for calling the _MockWorker obj's underlying member method code with example usage: obj.apply(fn) and returns: fn