code: def __len__(self):
      return self.num_epochs
  
imports: import dgl
  import numpy
  import torch
  import torch.nn
  import torch.nn.functional
  import tqdm
  from dgl.data.knowledge_graph import FB15k237Dataset
  from dgl.dataloading import GraphDataLoader
  from dgl.nn.pytorch import RelGraphConv
label_desc: Use image node_id 2 for calling the SubgraphIterator obj's underlying member method code with example usage: obj.__len__() and returns: self