After reading the comments, my decision has been to just discard any received string from the serial port that has this '\x00' sequence inside of it.
This is the function I have used in the code and works nicely:
def verify_string(self,texto_var): flag = 0 if '\x00' in texto_var: flag = 1 print("Invalid string received:", repr(texto_var)) self.tiempo_valor = 0 elif texto_var == "" or texto_var =='\n': print("do nothing") else: print("Valid string:", repr(texto_var)) # Do the convertion to int self.tiempo_valor = int(self.tiempo_texto.get()) return flag