There has GOT to be a better way to identify what is wrong with the challenge instead of just "Bummer! Try again!"

Beating my head on the wall again!
Assuming a hand size of 5 for Yatzy, checking to see that the _score_set returns truthy for five values, should be enough. I tried checking that the hand size was 5.

I tried testing with 7 different hands. hand[:] = [one, three, three, four, four] hand2[:] = [one, one, one, one] hand3[:] = [one, one, one, two] hand4[:] = [one, one, one, one, one] hand5[:] = [one, one, one, one, two] hand6[:] = [one, one, one, one, one, one] hand7[:] = [one, one, one, one, one, two]

When hand size wasn't limited to 5, both hand4 and hand7 returned 50. When hand size was limited to 5, only hand4 returned 50.

class YatzyScoresheet:
    def score_ones(self, hand):
        return sum(hand.ones)

    def _score_set(self, hand, set_size):
        scores = [0]
        for worth, count in hand._sets.items():
            if count == set_size:
                scores.append(worth*set_size)
        return max(scores)

    def score_one_pair(self, hand):
        return self._score_set(hand, 2)

    def score_chance(self, hand):
        return sum(hand)

    def score_yatzy(self, hand):
        #if len(hand) == 5 and self._score_set(hand, 5):
        if self._score_set(hand, 5):
            return 50
        return 0