code: def get_asset_address(self, asset: str) -> bytes:
          
          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.'))
docs: 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.