デフォルト引数

すみません、デフォルト引数を使わないまま
解答しました。。。

class Ghest():
    def __init__(self):
        #初期化
        self.sum = 0

    def take_food(self, price):
        self.sum += int(price)
    def take_softdrink(self, price):
        self.sum += int(price)

    def take_alcohol(self, price):
        pass
    def get_sum(self):
        return self.sum

class Adult(Ghest):
    def __init__(self):
        super().__init__()
        #初期化
        self.alcohol = False
    def take_food(self, price):
        if self.alcohol:
            self.sum += int(price) - 200
        else:
            self.sum += int(price)
    def take_alcohol(self,price):
        self.sum += int(price)
        self.alcohol = True

N, K = map(int,input().split())
ghests = [None] * N

for i in range(N):
    age = int(input())
    if age >= 20:
        ghests[i] = Adult()
    else:
        ghests[i] = Ghest()

#注文リスト(0=number,1=order,2=price)
for _ in range(K):
    order = input().split()
    if order[1] == "food":
        ghests[int(order[0])-1].take_food(int(order[2]))
    elif order[1] == "softdrink":
        ghests[int(order[0])-1].take_softdrink(int(order[2]))
    elif order[1] == "0":
        ghests[int(order[0])-1].take_alcohol(500)  
    else:
        ghests[int(order[0])-1].take_alcohol(int(order[2]))

#結果
for ghest in ghests:
    print(ghest.get_sum())

デフォルト引数使うと

class Ghest():
    def __init__(self):
        #初期化
        self.sum = 0

    def take_food(self, price):
        self.sum += int(price)
    def take_softdrink(self, price):
        self.sum += int(price)
    #ここでデフォルト引数追加
    def take_alcohol(self, price=500):
        pass
    def get_sum(self):
        return self.sum

class Adult(Ghest):
    def __init__(self):
        super().__init__()
        #初期化
        self.alcohol = False
    def take_food(self, price):
        if self.alcohol:
            self.sum += int(price) - 200
        else:
            self.sum += int(price)
    def take_alcohol(self, price=500):
        self.sum += int(price)
        self.alcohol = True

N, K = map(int,input().split())
ghests = [None] * N

for i in range(N):
    age = int(input())
    if age >= 20:
        ghests[i] = Adult()
    else:
        ghests[i] = Ghest()

#注文リスト(0=number,1=order,2=price)
for _ in range(K):
    order = input().split()
    if order[1] == "food":
        ghests[int(order[0])-1].take_food(int(order[2]))
    elif order[1] == "softdrink":
        ghests[int(order[0])-1].take_softdrink(int(order[2]))
    elif order[1] == "0":
        #ここの引数がなくなった
        ghests[int(order[0])-1].take_alcohol()  
    else:
        ghests[int(order[0])-1].take_alcohol(int(order[2]))

#結果
for ghest in ghests:
    print(ghest.get_sum())

とまあ、こんなふうな変化しかないですが
一応メモで