Extract labels from an MNIST file into integers.

  Args:
    filename: The path to an MNIST labels file.
    num_labels: The number of labels in the file.

  Returns:
    A int64 numpy array of shape [num_labels]

def _extract_mnist_labels(filename, num_labels):
  """Extract labels from an MNIST file into integers.

  Args:
    filename: The path to an MNIST labels file.
    num_labels: The number of labels in the file.

  Returns:
    A int64 numpy array of shape [num_labels]
  """
  with gzip.open(filename) as bytestream:
    bytestream.read(8)
    buf = bytestream.read(num_labels)
    labels = np.frombuffer(buf, dtype=np.uint8).astype(np.int64)
  return labels