code: def num_nodes_target(self):
      for key, item in self(
          "x_target", "pos_target", "norm_target", "batch_target"
      ):
          return item.size(self.__cat_dim__(key, item))
      return None
  
imports: import torch
  from typing import List, Optional
  from torch_geometric.data import Data
  from torch_geometric.data import Batch
  from torch_points3d.datasets.multiscale_data import MultiScaleBatch, MultiScaleData
  import re
label_desc: Use image node_id 4 for calling the Pair obj's underlying member method code with example usage: obj.num_nodes_target() and returns: None, item