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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 query_symbol(self, asset: str) -> str: """ This interface is used to query the asset's symbol of ONT or ONG. :param asset: a string which is used to indicate which asset's symbol we want to get. :return: asset's symbol in the form of string. """

        contract_address = self.get_asset_address(asset)
        method = 'symbol'
        invoke_code = build_native_invoke_code(contract_address, b'\x00', method, bytearray())
        tx = Transaction(0, 0xd1, int(time()), 0, 0, None, invoke_code, bytearray(), list())
        response = self.__sdk.rpc.send_raw_transaction_pre_exec(tx)
        symbol = ContractDataParser.to_utf8_str(response['Result'])
        return symbol