code: def sync_label_shape(self, it, verbose=False):
          
          assert isinstance(it, ImageDetIter), 'Synchronize with invalid iterator.'
          train_label_shape = self.label_shape
          val_label_shape = it.label_shape
          assert train_label_shape[1] == val_label_shape[1], "object width mismatch."
          max_count = max(train_label_shape[0], val_label_shape[0])
          if max_count > train_label_shape[0]:
              self.reshape(None, (max_count, train_label_shape[1]))
          if max_count > val_label_shape[0]:
              it.reshape(None, (max_count, val_label_shape[1]))
          if verbose and max_count > min(train_label_shape[0], val_label_shape[0]):
              logging.info('Resized label_shape to (%d, %d).', max_count, train_label_shape[1])
          return it
docs: Synchronize label shape with the input iterator. This is useful when
          train/validation iterators have different label padding.
  
          Parameters
          ----------
          it : ImageDetIter
              The other iterator to synchronize
          verbose : bool
              Print verbose log if true
  
          Returns
          -------
          ImageDetIter
              The synchronized other iterator, the internal label shape is updated as well.
  
          Examples
          --------
          >>> train_iter = mx.image.ImageDetIter(32, (3, 300, 300), path_imgrec='train.rec')
          >>> val_iter = mx.image.ImageDetIter(32, (3, 300, 300), path.imgrec='val.rec')
          >>> train_iter.label_shape
          (30, 6)
          >>> val_iter.label_shape
          (25, 6)
          >>> val_iter = train_iter.sync_label_shape(val_iter, verbose=False)
          >>> train_iter.label_shape
          (30, 6)
          >>> val_iter.label_shape
          (30, 6)