code: def check_labels_file_header(filename):
    
    with tf.gfile.Open(filename, 'rb') as f:
      magic = read32(f)
      read32(f)  # num_items, unused
      if magic != 2049:
        raise ValueError('Invalid magic number %d in MNIST file %s' % (magic,
                                                                       f.name))
docs: Validate that filename corresponds to labels for the MNIST dataset.