simple python driver to communicate with USB relay module. It handles several versions with differents numbers of relays

USBRelays.py

import serial
import argparse
import logging

class USBRelays():
    class Relay():
        index = ...
        header = 0xA0
        def __init__(self, index, log):
            self.index = index+1
            self.log = log
        def setOutput(self, serial, value):
            chksum = self.header + self.index + value

            frame = bytearray()
            frame.append(self.header)
            frame.append(self.index)
            frame.append(value)
            frame.append(chksum)
            self.log.debug(f'{frame=}')
            serial.write(frame)
            
    def __init__(self, port, baud, relaysNum):
        self.log = logging.getLogger("USBRelays")
        self.log.addHandler(logging.StreamHandler())
        self.serial = serial.Serial(port, baud)
        self.relays = [self.Relay(i, self.log) for i in range(relaysNum)]

    def setOutput(self, relayNum, value):
        self.log.debug(f'set relay {relayNum} to {value}')
        self.relays[relayNum].setOutput(self.serial, value)


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("-p", "--port", help="serial port", default="/dev/ttyUSB0")
    parser.add_argument("-b", "--baud", help="serial port baudrate", type=int, default=9600)
    parser.add_argument("-n", "--relayNum", help="number of available relays", type=int, default=1)
    parser.add_argument("-r", "--relay", help="selected relay (start at 0)", type=int, default=0)
    parser.add_argument("-v", "--value", help="value to apply to the relay", type=int, default=1)
    parser.add_argument("-d", "--debug", help="print debug", action='store_true')
    args = parser.parse_args()

    USB = USBRelays(args.port, args.baud, args.relayNum)

    if args.debug:
        USB.log.setLevel(logging.DEBUG)

    USB.setOutput(args.relay, args.value)