How to use the mnemonic.mnemonic.PBKDF2_ROUNDS function in mnemonic

def to_seed(cls, mnemonic: str, passphrase: str = "", index: int = 0) -> bytes:
        mnemonic = cls.normalize_string(mnemonic)
        passphrase = cls.normalize_string(passphrase)
        passphrase = "mnemonic" + passphrase
        mnemonic = mnemonic.encode("utf-8")
        passphrase = passphrase.encode("utf-8")
        stretched = hashlib.pbkdf2_hmac("sha512", mnemonic, passphrase, PBKDF2_ROUNDS)
        return cls.derive(stretched[:64], index)