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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_asset_address(self, asset: str) -> bytes: """ This interface is used to get the smart contract address of ONT otr ONG. :param asset: a string which is used to indicate which asset's contract address we want to get. :return: the contract address of asset in the form of bytearray. """

        if asset.upper() == 'ONT':
            return self.__ont_contract
        elif asset.upper() == 'ONG':
            return self.__ong_contract
        else:
            raise SDKException(ErrorCode.other_error('asset is not equal to ONT or ONG.'))