code: def __init__(self, vocab_size):
      super(LossForPretraining, self).__init__()
      self.loss_fn = torch.nn.CrossEntropyLoss(ignore_index=-1)
      self.vocab_size = vocab_size
  
imports: import torch
label_desc: Use image node_id 1 to create a new LossForPretraining object from inherited base classes: torch.nn with example: obj = LossForPretraining(vocab_size)