import serial, time
    import tkinter
    import os








    def serialcmdw():
    os.system('clear')
    serialcmd = input("serial command: ")
    ser.write (serialcmd)
    serialcmdw()

    ser = serial.Serial()
    os.system('clear')
    ser.port = "/dev/cu.usbmodem4321"
    ser.baudrate = 9600
    ser.open()
    time.sleep(1)
    serialcmdw()

ser.write(str.encode('allon'))