docstr: Get pipeline layers for current stage.
code: def get_held_layers(self) -> List[nn.Module]:
      """Get pipeline layers for current stage."""
      assert self.pipeline_stage_manager is not None
  
      if self.model.__class__.__name__ == "GPT2Model":
          module = self.model
      else:
          module = self.model.transformer
      stage_manager = self.pipeline_stage_manager
  
      held_layers = []
      layers_per_stage = self.distribute_layers(
          len(module.h), stage_manager.num_stages
      )
      if stage_manager.is_first_stage():
          held_layers.append(module.wte)
          held_layers.append(module.wpe)
          held_layers.append(module.drop)
      start_idx, end_idx = self.get_stage_index(
          layers_per_stage, stage_manager.stage
      )
      held_layers.extend(module.h[start_idx:end_idx])
      if stage_manager.is_last_stage():
          held_layers.append(module.ln_f)
      return held_layers
  
imports: from functools import partial
  from typing import Callable, Dict, List
  from torch import Tensor, nn
  import colossalai.shardformer.layer
  from ..modeling.gpt2 import GPT2PipelineForwards, get_gpt2_flash_attention_forward, gpt2_sequence_parallel_forward_fn
  from .base_policy import ModulePolicyDescription, Policy, SubModuleReplacementDescription
label_desc: Use image node_id 5 for calling the GPT2Policy obj's underlying member method code with example usage: obj.get_held_layers() and returns: held_layers