from collections import deque
from functools import reduce
from typing import Iterable

import pytest


def stick_last_two(source: Iterable):
    deck = deque()
    for item in source:
        deck.append(item)
        if len(deck) >= 3:
            yield deck.popleft()
    yield reduce(lambda a, b: a + b, deck)


@pytest.mark.parametrize(
    'inp, expected', [
        ('1', ['1']),
        ('12', ['12']),
        ('123', ['1', '23']),
        ('1234', ['1', '2', '34']),
    ])
def test_stick_last_two(inp, expected):
    result = list(stick_last_two(inp))
    assert result == expected


if __name__ == '__main__':
    for corrected in stick_last_two('1'):
        print(corrected)