Why won’t pySerial write inside of my program?

So I have a program set up on my arduino nano which reads a single byte from the serial port and turns on an LED depending on whether or not the byte received was 1 or 0. I thoroughly tested this program, both on the Serial monitor and with pySerial in the python 3 shell, and it worked fine. But when I have a simple program like this:

import serial
SERIAL = serial.Serial("COM4", 9600)
SERIAL.write(b'1')

The board doesn’t do anything. What am I doing wrong that pySerial works in the python shell but not in a python program?

Answer

After you open the serial port, delay it for minimum a second, because the Arduino resets itself when you open the serial connection and doesn’t start reading from the serial immediately.

Example:

import serial
import time
SERIAL = serial.Serial(baudrate='115200', timeout=.2, port='com4') #this edit is not important
time.sleep(3) #sleep 3 seconds
SERIAL.write(b'1')