I am sending an Encoder value using Arduino ATMega168 with serial port and I am receiving the value in raspberry pi using

Question

I am sending and Encoder value using Arduino ATMega168 with serial port and I am receiving the value in raspberry pi using python serial, before decoding format was in this form:
b'\n'
b'\r\n'
b'0\r\n'
When we decoded the data the value at the end contained note symbol. Now everything is good, but when we rotate the POT encoder anticlockwise, Arduino sends negative values, but our python program receives only "-" sign. So how do we receive negative values properly?
import serial
import time, threading
import RPi.GPIO as GPIO
def slider_encoder():
ser=serial.Serial("/dev/ttyUSB0",9600) #change ACM number as found from ls /dev/tty/ACM*
ser.baudrate=9600
GPIO.setmode(GPIO.BOARD)
#GPIO.setup(11, GPIO.OUT)
while True: #do while
read_ser=ser.read()
if all(i not in (10, 13) for i in tuple(read_ser)):
read_ser = read_ser.decode("utf-8")
break
print(read_ser)
##
#### print("#########$