For문을 이용한 Dictionary의 key, item 접근

# method 1
for key, value in batch.items():
    if (exp_dim): batch[key] = batch[key].unsqueeze(0).cuda()
    else: batch[key] = batch[key].cuda()
    
# method 2
for _, (key, value) in enumerate(batch.items()):
    if (exp_dim): batch[key] = batch[key].unsqueeze(0).cuda()
    else: batch[key] = batch[key].cuda()