all.py

#Class attributes will belong to the class itself
class Item:
    pay_rate = 0.8 
    all = []
    def __init__(self, name: str, price: float, quantity=0):
        assert price >= 0, f"Price {price} is not greater than or equal to zero "
        assert quantity >= 0, f"Quantity {quantity} is not greater than or equal to zero "
        
        self.name = name
        self.price = price
        self.quantity = quantity

        # Actions to execut
        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

    # Representing your objects in your console
    def __repr__(self):
        return f"Item('{self.name}',{self.price},{self.quantity})"

item1 = Item("Phone", 100, 1)
item2 = Item("Laptop", 1000, 3)
item3 = Item("Cable", 10, 5)
item4 = Item("Mouse", 50, 5)
item5 = Item("Keyboard", 75, 5)

print(Item.all)