sol.py

def pair_sum(my_list, target):
    complements = {}
    for i in range(len(my_list)):
        rest = complements.get(my_list[i], None)
        if rest:
            return (rest[1], i)
        complements[target - my_list[i]] = (my_list[i], i)

def pair_sum_slow(my_list, target):
    for i in range(len(my_list)):
        rest = target - my_list[i]
        for j in range(i, len(my_list)):
            if my_list[j] == rest:
                return (i, j)

print(pair_sum([1,2,3,4,5],6))
print(pair_sum([-1, -1, -2, -4, -5, -9, -12, -13],-21))
print(pair_sum([1, -7, 2, 15, -11, 2], 42))
print(pair_sum([0, -7, 2, 15, -11, 2], 2))
print(pair_sum([1,1,2,1,1,1], 3))
print("-"*10)
print(pair_sum_slow([1,2,3,4,5],6))
print(pair_sum_slow([-1, -1, -2, -4, -5, -9, -12, -13],-21))
print(pair_sum_slow([1, -7, 2, 15, -11, 2], 42))
print(pair_sum_slow([0, -7, 2, 15, -11, 2], 2))
print(pair_sum_slow([1,1,2,1,1,1], 3))