Product, Cart, Order classes in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a Product class with a constructor.

LLD

class Product:
    def __init__(self, id, name, price):
        self.id = id
        self.name = name
        self.price = [1]

Drag options to blanks, or click blank then click option'

Acost

Bprice

Cid

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable name like 'cost' or 'name' instead of 'price'.

The constructor assigns the price parameter to the instance variable self.price.

2fill in blank

medium

Complete the code to add a product to the Cart's items list.

LLD

class Cart:
    def __init__(self):
        self.items = []
    def add_product(self, product):
        self.items.[1](product)

Drag options to blanks, or click blank then click option'

Aappend

Bremove

Cpop

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'remove' or 'pop' which remove items instead of adding.

To add an item to a list in Python, use the append method.

3fill in blank

hard

Fix the error in the Order class constructor to correctly assign the cart parameter.

LLD

class Order:
    def __init__(self, order_id, cart):
        self.order_id = order_id
        self.cart = [1]

Drag options to blanks, or click blank then click option'

Acart

Border_id

Cself.cart

Dorder

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning 'order_id' or 'self.cart' instead of the parameter 'cart'.

The constructor should assign the passed cart parameter to the instance variable self.cart.

4fill in blank

hard

Fill both blanks to create a method that calculates the total price of items in the cart.

LLD

class Cart:
    def __init__(self):
        self.items = []
    def total_price(self):
        return sum(item.[1] for item in self.[2])

Drag options to blanks, or click blank then click option'

Aprice

Bname

Citems

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' or 'id' instead of 'price' for summing.

The method sums the price attribute of each item in the items list.

5fill in blank

hard

Fill all three blanks to create an Order method that returns a dictionary of product names and their quantities.

LLD

class Order:
    def __init__(self, order_id, cart):
        self.order_id = order_id
        self.cart = cart
    def product_quantities(self):
        quantities = {}
        for item in self.cart.[1]:
            name = item.[2]
            quantities[name] = quantities.get(name, 0) + [3]
        return quantities

Drag options to blanks, or click blank then click option'

Aitems

Bname

C1

Dprice

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'price' instead of 'name' as key or incrementing by price instead of 1.

The method loops over items in the cart, uses the product name as key, and increments the count by 1.

Practice

1. Which class is responsible for storing the details like product ID, name, and price?

easy

A. Product class

B. Cart class

C. Order class

D. User class

Solution

1. Step 1: Understand the role of Product class

   The Product class stores item details such as ID, name, and price.

2. Step 2: Compare with other classes

   The Cart class holds selected products and quantities, and Order class records purchased items and status, not product details.

3. Final Answer:

   Product class -> Option A

4. Quick Check:

   Product details = Product class [OK]

Hint: Product details belong to Product class only [OK]

Common Mistakes:

• Confusing Cart with Product class
• Thinking Order stores product details
• Assuming User class stores product info

2. Which of the following is the correct way to add a product to a cart in a typical class design?

easy

A. order.addProduct(product, quantity)

B. product.addToCart(cart, quantity)

C. cart.addProduct(product, quantity)

D. cart.createOrder(product, quantity)

Solution

1. Step 1: Identify the class responsible for holding selected products

   The Cart class holds selected products and their quantities before purchase.

2. Step 2: Check method naming conventions

   Adding a product to a cart is typically done by calling a method on the Cart object, like addProduct(product, quantity).

3. Final Answer:

   cart.addProduct(product, quantity) -> Option C

4. Quick Check:

   Adding product to cart = cart.addProduct() [OK]

Hint: Add products via Cart methods, not Product or Order [OK]

Common Mistakes:

• Calling addToCart on Product class
• Using Order class to add products before purchase
• Confusing method names like createOrder in Cart

3. Given the following code snippet, what will be the total cost stored in the Order after checkout?

product1 = Product(id=1, name='Pen', price=2)
product2 = Product(id=2, name='Notebook', price=5)
cart = Cart()
cart.addProduct(product1, 3)
cart.addProduct(product2, 2)
order = Order(cart)
order.checkout()

medium

A. 16

B. 19

C. 10

D. 7

Solution

1. Step 1: Calculate total cost from cart products and quantities

   Pen price = 2, quantity = 3 -> 2 * 3 = 6
   Notebook price = 5, quantity = 2 -> 5 * 2 = 10
   Total = 6 + 10 = 16

2. Step 2: Check if any additional charges or taxes apply

   No extra charges mentioned, so total cost should be 16.

3. Final Answer:

   16 -> Option A

4. Quick Check:

   2*3 + 5*2 = 16 [OK]

Hint: Multiply price by quantity, then sum all products [OK]

Common Mistakes:

• Adding quantities instead of multiplying by price
• Mixing product prices and quantities incorrectly
• Ignoring one product's cost

4. Identify the error in this Order class method that calculates total cost:

class Order:
    def __init__(self, cart):
        self.cart = cart
        self.total = 0
    def calculate_total(self):
        for product, qty in self.cart.items():
            self.total += product.price * qty
        return self.total

medium

A. Returning total instead of printing it

B. Using self.cart.items() instead of self.cart.products.items()

C. Multiplying price by quantity incorrectly

D. Not resetting self.total before calculation

Solution

1. Step 1: Analyze total calculation logic

   The method adds product price times quantity to self.total in a loop.

2. Step 2: Check for accumulation errors

   Since self.total is not reset before calculation, repeated calls will add to previous total, causing incorrect sums.

3. Final Answer:

   Not resetting self.total before calculation -> Option D

4. Quick Check:

   Reset total before sum to avoid accumulation [OK]

Hint: Reset totals before summing to avoid repeated addition errors [OK]

Common Mistakes:

• Assuming cart.items() is invalid without context
• Thinking multiplication is wrong when it is correct
• Confusing return with print for output

5. You want to design a system where a Cart can hold multiple Products with quantities, and an Order records the purchased items and status. Which design choice best supports scalability and clear responsibility?

hard

A. Make Cart store product IDs only; Order stores full product details and quantities

B. Make Cart hold Product objects with quantities; Order copies Cart items and tracks status separately

C. Make Product class hold quantity and add methods to update Cart and Order directly

D. Make Order class inherit from Cart and add status and total cost fields

Solution

1. Step 1: Understand separation of concerns

   Cart should hold selected products and quantities before purchase. Order should record purchased items and status separately.

2. Step 2: Evaluate design options for scalability and clarity

   Make Cart hold Product objects with quantities; Order copies Cart items and tracks status separately keeps Cart holding Product objects with quantities, and Order copies these items to keep a snapshot and track status, which is clean and scalable.

3. Final Answer:

   Make Cart hold Product objects with quantities; Order copies Cart items and tracks status separately -> Option B

4. Quick Check:

   Separate Cart and Order responsibilities for scalability [OK]

Hint: Keep Cart and Order responsibilities separate and clear [OK]

Common Mistakes:

• Making Order inherit Cart causing tight coupling
• Storing only product IDs in Cart losing details
• Putting quantity in Product class mixing concerns