code: def backward(self):
      self.losses["total_loss"].backward()
  
imports: import torch
  import tqdm
  from ..utils import common_functions
  from ..utils import loss_tracker
  from ..utils.key_checker import KeyChecker, KeyCheckerDict
label_desc: Use image node_id 16 for calling the BaseTrainer obj's underlying member method code with example usage: obj.backward() without return types