Arduino and Raspberry Pi Serial communication + multiple variables

it helps some times i have solved my problem.There was a time gap to access the value, i just had to add a while loop in order to get the value. In my arduino code i have added a delay in line no 24.

wish of those help When using readline with Python Serial the documentation states

arduino8 = serial.Serial(port, baudrate=brate, timeout=None)

To fix the issue you can do The problem is that you're comparing an int to a string. In the function read_from_device, this line:

    while ord(current_char) != MSG_START_CHAR: 

def read_from_device(serial_connection):  
    while serial_connection.read() != MSG_START_CHAR:
        pass

    response = ""
    while True:
        current_char = serial_connection.read()
        if current_char == MSG_END_CHAR:
            break
        response = response + current_char 
    return response

I wish this helpful for you Seems like the USB-Port on my Arduino UNO was damaged.
I tried different cables but got the same result. However, switching to an Arduino Micro solved the Problem.

around this issue Serial communication is always done in Bytes. So whatever you send through your interface will be received as a sequence of Bytes. As you encoded your "3" as UTF-8 it will be sent as 0x33 (51). Your "2" is 0x32 (50) respectively.
Increasing the baudrate as suggested in a comment won't help you as it will only increase the speed data is transmitted/received. Without a measurement you won't notice a difference betweeen sending a single byte with 9600 or 115200 baud.

void loop() {
  // send data only when you receive data:
  if (Serial.available() > 0) {
    // read the incoming byte:
    incomingByte = Serial.read();

    // say what you got:
    Serial.print("I received: ");
    Serial.println(incomingByte, DEC);
  }
}