Python websocket server, understanding difficulties in OOP

Question

I am trying to improvise a simple WebAPI control using pymodbus, I would like to implement this using websocket. From an example I found on the net, this was tried with the SimpleWebSocketServer module.

Now I have difficulties with the implementation, because I don't know exactly how to work with the class "class Echo(WebSocket):" correctly.

I think I should differentiate the variable "self.data" outside the class "Echo" which is passed from my websocket client using If comparisons?

The problem seems to be that the library pymodbus is not included in the "class echo". Anyway, the program terminates as soon as one of the four variables [relays1, relays1off, relays2, relays2off] is passed by the client. Or rather it does not abort but the socket connection is closed.

Unfortunately I am still relatively inexperienced in OOP, please could someone help me further.

The source of my websocket example is: https://iosoft.blog/2019/07/17/websocket-programming/

Kind regards!

# Websocket

import time
from pymodbus.client.sync import ModbusTcpClient as ModbusClient

UNIT = 0x1
HOST = '192.168.0.50'
PORT = 502
COILBASE = 512 # Coil Output Base Address

import signal, sys
from SimpleWebSocketServer import WebSocket, SimpleWebSocketServer

PORTNUM = 8001
#state = 0

def main():
    client = ModbusClient(host=HOST, port=PORT)
    client.connect()


# Websocket class to echo received data
class Echo(WebSocket):

    def handleMessage(self):
        print("Echoing '%s'" % self.data)
        self.sendMessage(self.data)

#        command = self.data
#        print(command)
#        return command
         return self.data

#        if self.data == "relaiys1":
#            print("debug")
#            rq = client.write_coil(COILBASE + 0, True, unit= UNIT)
#            print("debug")
#        elif self.data() == relays1off:
#            rq = client.write_coil(COILBASE + 0, False, unit= UNIT)

#        elif self.data() == relays2:
#            rq = client.write_coil(COILBASE + 1, True, unit= UNIT)

#        elif self.data() == relays2off:
#            rq = client.write_coil(COILBASE + 1, False, unit= UNIT)

    def handleConnected(self):
        print("Connected")

    def handleClose(self):
        print("Disconnected")


if self.data == "relaiys1":
    print("debug")
    rq = client.write_coil(COILBASE + 0, True, unit= UNIT)
    print("debug")
elif self.data() == relays1off:
    rq = client.write_coil(COILBASE + 0, False, unit= UNIT)

elif self.data() == relays2:
    rq = client.write_coil(COILBASE + 1, True, unit= UNIT)

elif self.data() == relays2off:
    rq = client.write_coil(COILBASE + 1, False, unit= UNIT)


# Handle ctrl-C: close server
def close_server(signal, frame):
    server.close()
    client.close()
    sys.exit()

if __name__ == "__main__":
    main()
    print("Websocket server on port %s" % PORTNUM)
    server = SimpleWebSocketServer('', PORTNUM, Echo)
    signal.signal(signal.SIGINT, close_server)
    server.serveforever()