How to use the fastecdsa._ecdsa.sign function in fastecdsa

pub_key = private.public()
        secret = private.secret

        if not k:
            if use_rfc6979 and USE_FASTECDSA:
                rfc6979 = RFC6979(tx_hash, secret, secp256k1_n, hashlib.sha256)
                k = rfc6979.gen_nonce()
            else:
                global rfc6979_warning_given
                if not USE_FASTECDSA and not rfc6979_warning_given:
                    _logger.warning("RFC6979 only supported when fastecdsa library is used")
                    rfc6979_warning_given = True
                k = random.SystemRandom().randint(1, secp256k1_n - 1)

        if USE_FASTECDSA:
            r, s = _ecdsa.sign(
                tx_hash,
                str(secret),
                str(k),
                str(secp256k1_p),
                str(secp256k1_a),
                str(secp256k1_b),
                str(secp256k1_n),
                str(secp256k1_Gx),
                str(secp256k1_Gy)
            )
            if int(s) > secp256k1_n / 2:
                s = secp256k1_n - int(s)
            return Signature(r, s, tx_hash, secret, public_key=pub_key, k=k)
        else:
            sk = ecdsa.SigningKey.from_string(private.private_byte, curve=ecdsa.SECP256k1)
            tx_hash_bytes = to_bytes(tx_hash)