Solution to the 3-SUM problem in Python.

test_threesum.py

from threesum import three_sums

def test_three_sums():
    integers = [2, 4, 8, 10, -7, -10, -25]
    expected = [(-10, 2, 8)]
    actual = list(three_sums(integers))
    assert [sorted(t) for t in three_sums(integers)] == [[-10, 2, 8]]

threesum.py

from collections import deque


def three_sums(iterable):
    S = sorted(iterable)
    for a, slice in zip(S, (deque(S[i:]) for i in range(1, len(S) - 1))):
        while slice:
            b = slice[0]
            c = slice[-1]
            if a + b + c == 0:
                yield a, b, c
            if a + b + c <= 0:
                slice.popleft()
            if a + b + c >= 0:
                slice.pop()


def has_three_sum(iterable):
    return sum(1 for s in three_sums(iterable)) > 0