Class Device encoding BUG

[AdrianDi91]

Dear Python for the Lab Community,

I followed the steps of the book PFTL until the End of Chapter 3.5.1 (page 35-39) but my connection to the Arduino Due is not working.
Not only that I was copying/writting the code from the book also the GitHub Version is not working in my case. Moreover it causes the same problem independent if it is running in windows or linux. I tried to find the problem by print debugging and the code looks like this now:

import serial
from time import sleep

class Device:
DEFAULTS = {'write_termination': '\n',
'read_termination': '\n',
'encoding': 'Ascii',
'baudrate': 9600,
'read_timeout': 1,
'write_timeout': 1,
}

def __init__(self, port):
    self.port = port
    self.rsc = None

def initialize(self):
        self.rsc = serial.Serial(port=self.port,                     #communication with the device
            baudrate=self.DEFAULTS['baudrate'],
            timeout=self.DEFAULTS['read_timeout'],
            write_timeout= self.DEFAULTS['write_timeout'])
        sleep(1)

def idn(self):                          # die Methode IDN sagt nur aus welcher COMPORT gelesen wird (für serial number)
    return self.query('*IDN?')

def get_analog_input(self, channel):
    message = f'IN:CH{channel}' #.format(channel)           # form message you want to send to device as string IN=Input
    print("Message ",type(message))
    print("Message: ", message)
    ans = self.query(message)
    print(f"Answer is {type(ans)} and {ans}")
    ans = int(ans)
    return ans         

def set_analog_output(self, channel, output_value):
    message = 'OUT:CH{}:{}'.format(channel, output_value)
    self.query(message)

def query(self, message):                                   # Query = Rückfrage
    message = message + self.DEFAULTS['write_termination']  #hier kommt 'n rein
    print("Print 1: ", message)
    message = message.encode(self.DEFAULTS['encoding'])     # hier encoding ascii encodes the string to bytes (like b)
    print("Print 2: ", message)
    self.rsc.write(message)                                 # writes to device
    ans = self.rsc.readline()
    print("ANS: ", ans)
    ans = ans.decode(self.DEFAULTS['encoding']).strip()     # return line with value
    print("ANS: ", ans)
    return ans

def finalize(self):
    if self.rsc is not None:
        self.rsc.close()

dev = Device('COM12') #<---- Remember to change the port
dev.initialize()
serial_number = dev.idn()
print(f'The device serial number is: {serial_number}')

volts = dev.get_analog_input(0) #Analog input and output must have the same number
print(volts)
dev.set_analog_output(0, 1000)
volts = dev.get_analog_input(0)
print(volts)
dev.finalize() #Close communication"""

As seen in the picture the line "ans = int(ans)" causes trouble because I cannot transform an empty variable into an integer. Somewhere before the problem was happening by the encoding or decoding I guess?

Thank you for the support.