code: def __route_layer(
      self, y1: torch.Tensor, y2: Optional[torch.Tensor] = None
  ):
      if isinstance(y2, torch.Tensor):
          return torch.cat([y1, y2], 1)
      return y1
  
imports: from typing import Union, List, Tuple, Optional
  import torch
  import torch.nn
  import numpy
  from .utils import transform_prediction
label_desc: Use image node_id 3 for calling the YoloV3 obj's underlying member method code with example usage: obj.__route_layer(y1, y2) and returns: y1, torch