import tkinter
import serial
data= serial.Serial('com31','9600')
def on():
 data.write(b'H')
def off():
 data.write(b'L')
led=tkinter.Tk()
Button=tkinter.Button
text=tkinter.Text
on=Button(led, text="ON ", command=on,  height=10, width=25)
off=Button(led, text="OFF", command=off,height=10, width=25)
on.pack(side=tkinter.RIGHT)
off.pack(side=tkinter.LEFT)
led.mainloop()