code: def __init__(self, num_classes, key=None):
      super().__init__()
      self.loss_class = nn.CrossEntropyLoss()
      self.num_classes = num_classes
      self.ignore_index = self.loss_class.ignore_index
      self.key = key
  
file_path: PaddleOCR/ppocr/losses/vqa_token_layoutlm_loss.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from paddle import nn
  from ppocr.losses.basic_loss import DMLLoss
label_desc: Use image node_id 1 to create a new VQASerTokenLayoutLMLoss object from inherited base classes: nn with example: obj = VQASerTokenLayoutLMLoss(num_classes, key)