<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def transfer(self, asset: str, from_acct: Account, b58_to_address: str, amount: int, payer: Account, gas_limit: int, gas_price: int):
 """ This interface is used to send a transfer transaction that only for ONT or ONG. :param asset: a string which is used to indicate which asset we want to transfer. :param from_acct: a Account object which indicate where the asset from. :param b58_to_address: a base58 encode address which indicate where the asset to. :param amount: the amount of asset that will be transferred. :param payer: a Account object which indicate who will pay for the transaction. :param gas_limit: an int value that indicate the gas limit. :param gas_price: an int value that indicate the gas price. :return: hexadecimal transaction hash value. """

        tx = self.new_transfer_transaction(asset, from_acct.get_address_base58(), b58_to_address, amount,
                                           payer.get_address_base58(), gas_limit, gas_price)
        tx.sign_transaction(from_acct)
        if from_acct.get_address_base58() != payer.get_address_base58():
            tx.add_sign_transaction(payer)
        return self.__sdk.get_network().send_raw_transaction(tx)