[Python] How to implement a message with a custom function code in pymodbus?

I'm currently trying to implement a modbus request that has a custom function code. The implementation is based on this example: custom_message.py

import struct
from pymodbus.pdu import ModbusRequest, ModbusResponse
from pymodbus.client.sync import ModbusTcpClient

client = ModbusTcpClient('192.168.0.55')
connection = client.connect()

class CustomModbusResponse(ModbusResponse):
# some fancy decoding should be done here..
pass

class CustomModbusRequest(ModbusRequest):
function_code = 55

def __init__(self, address):
ModbusRequest.__init__(self)
self.address = address
self.count = 1

def encode(self):
return struct.pack('>HH', self.address, self.count)

def decode(self, data):
self.address, self.count = struct.unpack('>HH', data)

def execute(self, context):
if not (1 <= self.count <= 0x7d0):
return self.doException(ModbusExceptions.IllegalValue)
if not context.validate(self.function_code, self.address, self.count):
return self.doException(ModbusExceptions.IllegalAddress)
values = context.getValues(self.function_code, self.address,
self.count)
return CustomModbusResponse(values)

request = CustomModbusRequest(0)
result = client.execute(request)
print(result)


The request works as expected. I can see the correct response on the network layer. However I can't parse the result. Pymodbus is throwing the following error:

DEBUGymodbus.factory:Factory Response[55]
ERRORymodbus.factory:Unable to decode response Modbus Error: Unknown response 55
ERRORymodbus.transaction:Modbus Error: [Input/Output] Unable to decode request


The example states that in this case, I would have to:

If you implement a new method that is not currently implemented, you must register the request and response with a ClientDecoder factory.
​

Is there an elegant way to do this without patching the library?

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