ESP32 Devkit V4 LED is being shut off when writing data over serial

[bangell-rockhall]

This is a follow up question to this post: https://github.com/orgs/micropython/discussions/11096#discussion-4989105

I have this MicroPython class running on my esp32. I did try to simplify it a bit and not include code not relevant to my question.

from machine import Pin
import sys
import time
import uselect

led = Pin(2, Pin.OUT) 
serialPoll = uselect.poll()
serialPoll.register(sys.stdin, uselect.POLLIN)
serialBuffer = ""

def handle_command(message):
    """
    Handle a message received over serial.

    The message may contain multiple commands within it.
    Each command within the message will be split into separate submessages which will be handled one at a time.

    :param message: (string) The message to handle
    """
    if not message: # if the string is empty
        return 1
    if ("\n" in message):
            if submessage == "2on":
                led.on() # the led turns on
                time.sleep(1) # the led stays on for this time period
                sys.stdout.buffer.write("led on\n") # the led is turning off here for some reason when using the Python app but not with the Arduino IDE serial monitor
            else: # unrecognized message
                sys.stdout.buffer.write("error\n")
        global serialBuffer
        serialBuffer = ""


def read_serial():
    """
    Reads and returns all available data over serial.

    :return: Returns the character which were read, otherwise returns None
    """
    if serialPoll.poll(): # check the serialPoll every 10 milliseconds
        return sys.stdin.readline()
    else:
        return None


while True:
    # continuously read messages over serial and handle them
    serialData = read_serial()
    if serialData != None:
        serialBuffer += str(serialData)
        handle_command(serialBuffer)

When I test this code using the Arduino IDE's built in serial monitor the ESP32 behaves as intended. I am sending the message "2on" with the new line character selected from the drop down menu, and when I do that the onboard LED turns on and the ESP32 responds with "led on". I have attached an image below, there is not much to see, but basically I hit the restart button on the ESP32, so the ESP32 dumped a bunch of stuff to the monitor when restarting, then I typed "2on" into the message box (I did not actually type the quotation marks into the box, I just added those to try to make it clear what I typed), and hit enter. The LED turned on and the device responded with "led on".

When I try to recreate this using a Python app I wrote the ESP32 is not behaving as intended. When I run the python class which is shown below the LED on the ESP32 will turn on and stay on for 1 second (the time.sleep(1) is only there so I could test if the LED would stay on) and then after the time.sleep() has passed the LED turns off because of an unknown reason.

import serial
import time

# create a serial object
ser = serial.Serial(port = 'COM4',
                        baudrate = 115200,
                        bytesize = serial.EIGHTBITS,
                        parity = serial.PARITY_NONE,
                        stopbits = serial.STOPBITS_ONE,
                        timeout =  5)
time.sleep(2) # wait for the connection to establish

cmd = ("2on")
ser.write(cmd.encode()) # send "2on"
cmd = '\n'
ser.write(cmd.encode()) # send the newline character

response = ser.readline().decode().strip()
print("received response: " + response)
ser.close() # close the serial connection

I have also tried using the following command to send the data to the ESP32:

ser.write(b'2on\n') # send a command to the ESP32 and wait for the response

Another potentially helpful piece of information is that I have tried using the onboard LED (Pin 2 on the ESP32) as well as other external LEDs with the MicroPython code/ESP32 and the behavior is the same either way.

What I would like to know is why is the LED on the ESP32 turning off when I use the Python app, as well as how can I resolve that problem.