class Solution(object):
    def two_sum(self, arr, target):
        if not arr:
            return None

        remainders = dict()
        for i, num in enumerate(arr):
            if target - num in remainders:
                return (remainders[target - num], i)
            remainders[num] = i

solution = Solution()
print(solution.two_sum([1, 3, 5, 9], 10))