import struct

 class ModbusCodeC():

     """

     This CodeC class implement partly of Modbus encode and decode

     The chamber only offer 03H and 06H function-code for using

     """

     @staticmethod

     def MBAP_encode():

         transFlagHi = b'\x00'

         transFlagLo = b'\x00'

         protoFlag = b'\x00\x00'

         length = b'\x00\x06'

         unitFlag = b'\x00'

         mbap = transFlagHi + transFlagLo + protoFlag + length + unitFlag

         return mbap

     @staticmethod

     def PDU_encode(func, regi, num=1, data=None):

         funcList = {'r': b'\x03',

                     'w': b'\x06'}

         funcCode = funcList[func]

         registerStart = struct.pack('!H', regi)

         registerNum = struct.pack('!H', num)

         if data and func == 'w':

             dataCode = struct.pack('!H', data)

             pdu = funcCode + registerStart + dataCode

             return pdu

         pdu = funcCode + registerStart + registerNum

         return pdu

     @staticmethod

     def encode(func, regi, num, data=None):

         return ModbusCodeC.MBAP_encode() + ModbusCodeC.PDU_encode(func, regi, num, data)

     @staticmethod

     def MBAP_decode(s):

         m = {}

         m['transFlagHi'] = s[:1]

         m['transFlagLo'] = s[1:2]

         m['protoFlag'] = s[2:4]

         m['length'] = s[4:6]

         m['unitFlag'] = s[6:]

         return m

     @staticmethod

     def PDU_decode(s):

         p = {}

         '''

         p['funcCode'] = s[:1]

         p['registerStart'] = s[1:3]

         p['registerNum'] = s[3:5]

         p['data'] = s[5:]

         '''

         # TODO: Add bit number and data length check here

         p['funcCode'] = s[:1]

         p['bitNum'] = s[1:2]

         p['data'] = s[2:]

         return p

     @staticmethod

     def decode(msg):

         msg_de = {}

         mbap, pdu = msg[:7], msg[7:]

         msg_de['MBAP'] = ModbusCodeC.MBAP_decode(mbap)

         msg_de['PDU'] = ModbusCodeC.PDU_decode(pdu)

         return msg_de

 if __name__ == '__main__':

     print(ModbusCodeC.encode('r', 5, 3))

     print(ModbusCodeC.encode('w', 5, 1, 8))