def calculate(liste): my_sum = 0 for n in liste: val = n * 2 if val >= 10: x, y = str(val) my_sum += (int(x) + int(y)) else: my_sum += val return my_sum def is_valid(number): result = 0 result += calculate(map(int, number[1::2])) result += sum(map(int, number[0::2])) return result%10==0 print(is_valid("972487086"))