code: def _return_actor(self, actor):
      self._idle_actors.append(actor)
      if self._pending_submits:
          self.submit(*self._pending_submits.pop(0))
  
imports: import copy
  import logging
  from functools import partial
  from typing import Any, Callable, Dict, Generator, List, Optional, Tuple, Union
  import numpy
  from scipy import sparse
  import ray
label_desc: Use image node_id 8 for calling the ActorPool obj's underlying member method code with example usage: obj._return_actor(actor) without return types