code: def crypto_box_seed_keypair(seed):
      
      ensure(isinstance(seed, bytes),
             "seed must be bytes",
             raising=TypeError)
  
      if len(seed) != crypto_box_SEEDBYTES:
          raise exc.ValueError("Invalid seed")
  
      pk = ffi.new("unsigned char[]", crypto_box_PUBLICKEYBYTES)
      sk = ffi.new("unsigned char[]", crypto_box_SECRETKEYBYTES)
  
      rc = lib.crypto_box_seed_keypair(pk, sk, seed)
      ensure(rc == 0,
             'Unexpected library error',
             raising=exc.RuntimeError)
  
      return (
          ffi.buffer(pk, crypto_box_PUBLICKEYBYTES)[:],
          ffi.buffer(sk, crypto_box_SECRETKEYBYTES)[:],
      )
docs: Returns a (public, secret) keypair deterministically generated
      from an input ``seed``.
  
      .. warning:: The seed **must** be high-entropy; therefore,
          its generator **must** be a cryptographic quality
          random function like, for example, :func:`~nacl.utils.random`.
  
      .. warning:: The seed **must** be protected and remain secret.
          Anyone who knows the seed is really in possession of
          the corresponding PrivateKey.
  
  
      :param seed: bytes
      :rtype: (bytes(public_key), bytes(secret_key))