simple python driver to communicate with USB relay module based on FTDI chip like https://www.sainsmart.com/products/4-channel-5v-usb-relay-module

FTDIRelays.py

from pyftdi.gpio import GpioController
import argparse

class FTDIRelays:
    def __init__(self):
        self._gpio = GpioController()
        self._state = 0  # SW cache of the GPIO output lines
        
    def pins(self):
        print(self._gpio.direction)
    
    def open(self, out_pins):
        """Open a GPIO connection, defining which pins are configured as
           output and input"""
        out_pins &= 0xFF
        self._gpio.configure('ftdi:///1', direction=out_pins, frequency=1e3,
                       initial=0x0)
        self._state = self._gpio.read_port()
        print('%x' % self._state)
        
    def close(self):
        """Close the GPIO connection"""
        self._gpio.close()
        
    def get_gpio(self, line):
        """Retrieve the level of a GPIO input pin
           :param line: specify which GPIO to read out.
           :return: True for high-level, False for low-level
        """
        value = self._gpio.read_port()
        print(value)
        return bool(value & (1 << line))
        
    def set_gpio(self, line, on):
        """Set the level of a GPIO ouput pin.
           :param line: specify which GPIO to madify.
           :param on: a boolean value, True for high-level, False for low-level
        """
        if on != 0:
            state = self._state | (1 << line)
        else:
            state = self._state & ~(1 << line)
        self._commit_state(state)

        
    def _commit_state(self, state):
        """Update GPIO outputs
        """
        self._gpio.write_port(state)
        # do not update cache on error
        self._state = state
        print('%x' % self._state)

        

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    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)
    args = parser.parse_args()

    device = FTDIRelays()
    device.open(0x0f)

    print("set relay " + str(args.relay) + " to " + str(args.value))
    device.set_gpio(args.relay, args.value)