code: def extract_labels(filename):
      
      with gzip.open(filename) as bytestream:
          magic = _read32(bytestream)
          if magic != 2049:
              raise ValueError(
                  'Invalid magic number %d in MNIST label file: %s' %
                  (magic, filename))
          num_items = _read32(bytestream)
          buf = bytestream.read(num_items)
          labels = numpy.frombuffer(buf, dtype=numpy.uint8)
          return labels
docs: Extract the labels into a 1D uint8 numpy array [index].