All, I want define an int(987654321) <= [9, 8, 7, 6, 5, 4, 3, 2, 1] convertor, if the length of int number < 9, for example 10 the list will be [0,0,0,0,0,0,0,1,0] , and if the length 9, for example 9987654321 , the list will be [9, 9, 8, 7, 6, 5, 4, 3, 2, 1] >>> i 987654321 >>> l [9, 8, 7, 6, 5, 4, 3, 2, 1] >>> z = [0]*(len(unit) - len(str(l))) >>> z.extend(l) >>> l = z >>> unit [100000000, 10000000, 1000000, 100000, 10000, 1000, 100, 10, 1] >>> sum([x*y for x,y in zip(l, unit)]) 987654321 >>> int("".join([str(x) for x in l])) 987654321 >>> l1 = [int(x) for x in str(i)] >>> z = [0]*(len(unit) - len(str(l1))) >>> z.extend(l1) >>> l1 = z >>> l1 [9, 8, 7, 6, 5, 4, 3, 2, 1] >>> a = [i//x for x in unit] >>> b = [a[x] - a[x-1]*10 for x in range(9)] >>> if len(b) = len(a): b[0] = a[0] # fix the a[-1] issue >>> b [9, 8, 7, 6, 5, 4, 3, 2, 1] I tested above solutions but found those may not faster/simple enough than I want and may have a length related bug inside, anyone may share me a better solution for this kinds convertion? Thanks!