def derive_private_key(self, sequence):
encoded = "<STR_LIT>" % (str(self), sequence)<EOL>a = bytes(encoded, "<STR_LIT:ascii>")<EOL>s = hashlib.sha256(hashlib.sha512(a).digest()).digest()<EOL>return PrivateKey(hexlify(s).decode("<STR_LIT:ascii>"), prefix=self.pubkey.prefix)<EOL>
Derive new private key from this private key and an arbitrary
            sequence number