code: def get_value(self, key: Optional[EdgeType] = None) -> Optional[int]:
      if self.value is None or isinstance(self.value, int):
          return self.value
  
      assert isinstance(key, tuple) and len(key) == 3
      if key not in self.value:
          num_src_nodes = self.num_nodes.get_value(key[0])
          num_dst_nodes = self.num_nodes.get_value(key[-1])
          assert num_src_nodes is not None and num_dst_nodes is not None
          self.value[key] = num_src_nodes * num_dst_nodes
  
      return self.value[key]
  
imports: from abc import ABC, abstractmethod
  from dataclasses import dataclass
  from typing import Any, Callable, Dict, List, Optional, Tuple, Union
  import torch
  import torch.nn.functional
  from torch_geometric.data import Data, HeteroData
  from torch_geometric.data.datapipes import functional_transform
  from torch_geometric.data.storage import EdgeStorage, NodeStorage
  from torch_geometric.transforms import BaseTransform
  from torch_geometric.typing import EdgeType, NodeType
label_desc: Use image node_id 2 for calling the _NumEdges obj's underlying member method code with example usage: obj.get_value(key) and returns: self, self