code: def derive_from_seed(self, offset):
          
          seed = int(hexlify(bytes(self)).decode("ascii"), 16)
          z = int(hexlify(offset).decode("ascii"), 16)
          order = ecdsa.SECP256k1.order
          secexp = (seed + z) % order
          secret = "%0x" % secexp
          if len(secret) < 64: # left-pad with zeroes
              secret = ("0" * (64-len(secret))) + secret
          return PrivateKey(secret, prefix=self.pubkey.prefix)
docs: Derive private key using "generate_from_seed" method.
              Here, the key itself serves as a `seed`, and `offset`
              is expected to be a sha256 digest.