So I have no idea how I need to word this but I've been told to ask a new question so here, edit the title accrdingly.

I need to do digitalWrite(7, HIGH); in Arduino when there is a Serial connection between Arduino and a Python program (PySerial) via USB. When the USB cable is disconnected, Arduino has to do do digitalWrite(7, LOW); How can I know when Serial connection is "established" and when it is "disconnected" in Arduino?

Here's the Arduino code:

void setup() {
  Serial.begin(9600);
  
  pinMode(7, INPUT_PULLUP);
}

void loop() {
    int val = digitalRead(7);
    if (val == HIGH) {
        Serial.print("1");
    } else {
        Serial.print("0");    
    }
    Serial.println("");  // new line
  
}

Python code:

import time
import serial

# setup Arduino USB communication
try:
    arduinoSerialData = serial.Serial('com3', 9600)
    
except: # not connected/damaged
    pass
    
while True:
    if arduinoSerialData.inWaiting() > 0:
        datastr = arduinoSerialData.readline()
        print datastr
        time.sleep(1)

WHat I want to add is, if Python program exits, or crashes, let the Arduino know somehow. More specifically turn on a LED in pin 8.