code: def num_anchors_per_location(self):
      # 计算每个预测特征层上每个滑动窗口的预测目标数
      return [
          len(s) * len(a)
          for s, a in zip(self.sizes, self.aspect_ratios)
      ]
  
imports: from typing import List, Optional, Dict, Tuple
  import torch
  from torch import nn, Tensor
  from torch.nn import functional
  import torchvision
  from .None import det_utils
  from .None import boxes
  from .image_list import ImageList
label_desc: Use image node_id 4 for calling the AnchorsGenerator obj's underlying member method code with example usage: obj.num_anchors_per_location() and returns: unknown