class_docstr: Actor to make resource requests to autoscaler for the datasets.
  
  The resource requests are set to timeout after RESOURCE_REQUEST_TIMEOUT seconds.
  For those live requests, we keep track of the last request made for each execution,
  which overrides all previous requests it made; then sum the requested amounts
  across all executions as the final request to the autoscaler.
code: def _purge(self):
      # Purge requests that are stale.
      now = time.time()
      for k, (_, t) in list(self._resource_requests.items()):
          if t < now:
              self._resource_requests.pop(k)
  
file_path: ray/python/ray/data/_internal/execution/autoscaling_requester.py
imports: import math
  import threading
  import time
  from typing import Dict, List
  import ray
  from ray.data.context import DataContext
  from ray.util.scheduling_strategies import NodeAffinitySchedulingStrategy
label_desc: Use image node_id 4 for calling the AutoscalingRequester obj's underlying member method code with example usage: obj._purge() without return types