code: def get_private(self):
          
          encoded = "%s %d" % (self.brainkey, self.sequence)
          a = _bytes(encoded)
          s = hashlib.sha256(hashlib.sha512(a).digest()).digest()
          return PrivateKey(hexlify(s).decode("ascii"), prefix=self.prefix)
docs: Derive private key from the brain key and the current sequence
              number