class Item:
    pay_rate = 0.8 # The pay after %20 discount
    all = []
    def __init__(self, name: str, price: float, quantity=0):
        #Run validations to the recieved arguments
        assert price >= 0, f"Price {price} is not greater than or equal tozero!"
        assert quantity >= 0, f"Quantity {quantity} is not greater than or equal to zero!"

        # Assign to self object
        self.name = name
        self.price = price
        self.quantity = quantity

        #Actions to execute

        Item.all.append(self)

    def calculate_total_price(self):
        return self.price * self.quantity

    def apply_discount(self):
        self.price = self.price * self.pay_rate

    @classmethod
    def instantiate_from_csv(cls):
        with open('items.csv', 'r') as f:
            reader = csv.DictReader(f)
            items = list(reader)
        for item in items:
        Item(
                name=item.get('name'),
                price=float(item.get('price')),
                quantity=int(item.get('quantity')),
            )
    @staticmethod
    def is_integer(num):
        #We will count out the floats that are .0
        if isinstance(num, float):
            #Count out the floats that are point zero
            return num.is_integer()
        elif isinstance(num, int):
            return True
        else:
            return False

    def __repr__(self):
        return f"Item('{self.name}', {self.price}, {self.quantity})"

我目前正在学习python，并试图理解OOP的概念。除了下面几行之外，我都理解了

def is_integer(num):
    #We will count out the floats that are .0
    if isinstance(num, float):
        #Count out the floats that are point zero
        return num.is_integer()
    elif isinstance(num, int):
        return True
    else:
        return False

有人能解释一下为什么num.is_integer（）返回False吗？该函数的定义目的是从100.0或50.0这样的浮点数中删除.0（教程中是这么说的）
这是我第一次遇到这种类型的返回用法。我习惯于返回a*B或返回'Hi'类型的东西。