code: def loss(self, pred, link_label):
      return self.loss_fn(pred, link_label)
  
imports: import copy
  import argparse
  import torch
  import torch.nn
  import torch.nn.functional
  import networkx
  import numpy
  import sklearn.metrics
  import torch_geometric.nn
  from torch.utils.data import DataLoader
  from deepsnap.dataset import GraphDataset
  from deepsnap.batch import Batch
label_desc: Use image node_id 4 for calling the Net obj's underlying member method code with example usage: obj.loss(pred, link_label) and returns: self