code: def check_pp_rank_valid(self, pp_rank: int) -> bool:
      return -1 < pp_rank < self._stage_num
  
imports: import threading
  from typing import List
  import torch.distributed
  from torch.distributed import rpc
  from colossalai.legacy.tensor import ProcessGroup
label_desc: Use image node_id 15 for calling the PipelineProcessGroup obj's underlying member method code with example usage: obj.check_pp_rank_valid(pp_rank) and returns: unknown