Can anyone explain this video a bit more?

class Hand(list):
    # certain number of dice all of the dice have to be the same kind of die
    # create a hand class to run different sets of dice
    # size: number of dice 
    def __init__(self, size=0, die_Class= None,  *args, **kwargs):
        if not die_class:
            raise ValueError("You must provide a die class")

        for _ in range(size):
            self.append(die_class())
        self.sort()

    def _by_value(self, value):
        dice = []
        for die in self:
            if die == value:
                dice.append(die)
    return dice
    # return a list with value as item

class YatzyHand(Hand):
    # extent hand 
    def __init__(self, *args, **kwargs):
        super().__init__(size=5, die_class=D6, *args, **kwargs)


    def _by__value(self, value):
        dice = []
        for die in self:
            if die == value:
                dice.append(die)
         return dice  

         @property
         def ones(self):
             return self._by__value(1)

         @property
         def twos(self):
             return self._by__value(2)

         @property
         def threes(self):
             return self._by__value(3)

         @property
         def fours(self):
             return self._by__value(4)

         @property
         def fives(self):
             return self._by__value(5)

         @property
         def sixs(self):
             return self._by__value(6)

       @property
       def _sets(self):
           return{
                   1: len(self.ones)
                   2: len(self.twos)
                   3: len(self.threes)
                   4:len(self.fours)
                   5:len(self.fives)
                   6:len(self.sixs)
                 }
          # _sets:dictionary
          # keys:value 
          # value: how many of that value in dice[]

# yatzy folder
# scoresheets.py
class YatzyScoresheet:
    def score_ones(self, hand):
        return sum(hand.ones) # size for value 1 

    def _score_set(self, hand, set_size):
    # set_size is a setted size:len(self.n), such as self.two
        scores = []
        for worth, count in hand._sets.items():
            if count == set_size: 
                scores.append(worth*set_size)
                # scores: list with items: n*value such as [2*2, 2*5]
            #return sum(scores)  
             return max(scores)

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



from hands import YatzyHand
from dice import D6 
from Scoreesheets import YatzyScoresheet
hand = YatzyHand()
three = D6(value=3)
four = D6(value=4)
one = D6(value=1)
hand[:] = [one, three, three, four, four]
YatzyScoresheet().score_one_pair(hand)
8 # scores[3+3, 4+4], return 4+4 

# value: the face that show up  -> Die and D6
# size: the number of different value -> hand
# set: the number of certain value -> hand
# set < size  
# self._set: dictionary: value as dictionary's key and size(count) as dictionary's  value.
# set_size: a size set as selection constraint.
# score: list: the value * set_size 
# max(score) & sum(score) is function that used on a list