code: import time
  import torch
  from options.train_options import TrainOptions
  from data import create_dataset
  from models import create_model
  from util.visualizer import Visualizer
  
  
  if __name__ == '__main__':
      opt = TrainOptions().parse()   # get training options
      dataset = create_dataset(opt)  # create a dataset given opt.dataset_mode and other options
      dataset_size = len(dataset)    # get the number of images in the dataset.
  
      model = create_model(opt)      # create a model given opt.model and other options
      print('The number of training images = %d' % dataset_size)
  
      visualizer = Visualizer(opt)   # create a visualizer that display/save images and plots
      opt.visualizer = visualizer
      total_iters = 0                # the total number of training iterations
  
      optimize_time = 0.1
  
      times = []
      for epoch in range(opt.epoch_count, opt.n_epochs + opt.n_epochs_decay + 1):    # outer loop for different epochs; we save the model by <epoch_count>, <epoch_count>+<save_latest_freq>
          epoch_start_time = time.time()  # timer for entire epoch
          iter_data_time = time.time()    # timer for data loading per iteration
          epoch_iter = 0                  # the number of training iterations in current epoch, reset to 0 every epoch
          visualizer.reset()              # reset the visualizer: make sure it saves the results to HTML at least once every epoch
  
          dataset.set_epoch(epoch)
          for i, data in enumerate(dataset):  # inner loop within one epoch
              iter_start_time = time.time()  # timer for computation per iteration
              if total_iters % opt.print_freq == 0:
                  t_data = iter_start_time - iter_data_time
  
              batch_size = data["A"].size(0)
              total_iters += batch_size
              epoch_iter += batch_size
              torch.cuda.synchronize()
              optimize_start_time = time.time()
              model.set_input(data)         # unpack data from dataset and apply preprocessing
              if epoch == opt.epoch_count and i == 0:
                  model.data_dependent_initialize()
                  model.setup(opt)               # regular setup: load and print networks; create schedulers
                  model.parallelize()
              model.optimize_parameters()   # calculate loss functions, get gradients, update network weights
              torch.cuda.synchronize()
              optimize_time = (time.time() - optimize_start_time) / batch_size * 0.005 + 0.995 * optimize_time
  
              if total_iters % opt.display_freq == 0:   # display images on visdom and save images to a HTML file
                  save_result = total_iters % opt.update_html_freq == 0
                  model.compute_visuals()
                  visualizer.display_current_results(model.get_current_visuals(), epoch, save_result)
  
              if total_iters % opt.print_freq == 0:    # print training losses and save logging information to the disk
                  losses = model.get_current_losses()
                  visualizer.print_current_losses(epoch, epoch_iter, losses, optimize_time, t_data)
                  if opt.display_id is None or opt.display_id > 0:
                      visualizer.plot_current_losses(epoch, float(epoch_iter) / dataset_size, losses)
  
              if total_iters % opt.save_latest_freq == 0:   # cache our latest model every <save_latest_freq> iterations
                  print('saving the latest model (epoch %d, total_iters %d)' % (epoch, total_iters))
                  print(opt.name)  # it's useful to occasionally show the experiment name on console
                  save_suffix = 'iter_%d' % total_iters if opt.save_by_iter else 'latest'
                  model.save_networks(save_suffix)
  
              iter_data_time = time.time()
  
          if epoch % opt.save_epoch_freq == 0:              # cache our model every <save_epoch_freq> epochs
              print('saving the model at the end of epoch %d, iters %d' % (epoch, total_iters))
              model.save_networks('latest')
  #             model.save_networks(epoch)
  
          print('End of epoch %d / %d \t Time Taken: %d sec' % (epoch, opt.n_epochs + opt.n_epochs_decay, time.time() - epoch_start_time))
          model.update_learning_rate()                     # update learning rates at the end of every epoch.
  
apis: torch.cuda.synchronize