def transform_letter_in_number(letter): return ord(letter) - 64 def isNumberValid(idNumber): strIdNumberWith2First = "" for i in range(len(idNumber)): if i == 0 or i == 1: strIdNumberWith2First += str(transform_letter_in_number(idNumber[i])) else: strIdNumberWith2First += str(idNumber[i]) idNumberWith2First = int(strIdNumberWith2First) reste = idNumberWith2First % 9 if reste == 7: return True else: return False idNumber = "UF9052784116" print(isNumberValid(idNumber))