Notebook

Shopping Cart App¶

Build a shopping cart application that tracks items, their prices, and calculates totals. This assignment will practice dictionaries, lists, functions, and user interaction.

Core Requirements¶

Your shopping cart app must track both items and their costs using dictionaries.

Part 1: Basic Functions¶

Write the following functions:

display_cart(cart) - Shows all items with prices and total

# Example output:
Shopping Cart:
1. Milk - 3.99
2. Bread - 2.49
3. Eggs - 4.99

Total: $11.47

add_to_cart(cart, item, price) - Adds an item with its price
- If item already exists, update the price (ask user to confirm)
- Return True if added/updated, False otherwise
remove_from_cart(cart, item_number) - Removes item by position
- Remember: display shows 1-based numbers!
- Return the price of removed item (or 0 if invalid)
calculate_total(cart) - Returns the total cost of all items

Part 2: Main Program¶

Create a menu-driven program:

=== SHOPPING CART ===
Current total: $0.00

1. View cart
2. Add item
3. Remove item
4. Clear cart
5. Checkout

Enter choice:

Requirements:

Show current total in the menu
The program should loop until user chooses checkout
Handle invalid menu choices gracefully
Start with an empty cart (empty dictionary)
Validate that prices are positive numbers

Sample Interaction¶

=== SHOPPING CART ===
1. View cart
2. Add item
3. Remove item
4. Clear cart
5. Checkout

Enter choice: 2
Enter item name: Milk
Enter price: 3.99
Added Milk (3.99) to cart!

Enter choice: 2
Enter item name: Bread
Enter price: 2.49
Added Bread (2.49) to cart!

Enter choice: 1

Shopping Cart:
1. Milk - 3.99
2. Bread - 2.49
Total: 6.48

Enter choice: 2
Enter item name: Milk
Milk is already in cart at 3.99
Enter new price (or 0 to cancel): 4.29
Updated Milk to 4.29

Enter choice: 5

Final Shopping Cart:
1. Milk - 4.29
2. Bread - 2.49
Total: $6.78
Thank you for shopping!

Bonus Features¶

Level 1: Enhanced Features¶

Add quantity tracking:
- Store both price per item and quantity
- Display as Milk - 3.99 x 2 = 7.98
- Update calculate_total() to handle quantities
Add discount codes:
- Create a dictionary of valid codes and discount percentages
- Apply discount at checkout
Show savings when updating prices (if new price is lower)

Level 2: Store Catalog¶

Create a pre-defined product catalog dictionary:

catalog = {
    "milk": 3.99,
    "bread": 2.49,
    "eggs": 4.99,
    # ... more items
}

When adding items, allow user to:
- Choose from catalog (show available items)
- Or add custom item with custom price
Validate items against catalog for pricing consistency

Level 3: Receipt Generation¶

Create a generate_receipt(cart) function that produces:

========== RECEIPT =======
Date: 2024-01-15

Milk................. 3.99
Bread................ 2.49
Eggs (x2)............ 9.98

Subtotal:            16.46
Tax (8%):             1.32
--------------------------
TOTAL:               17.78

Thank you for shopping!
==========================

Tips¶

Use a dictionary to store items as keys and prices as values
To get a numbered list from a dictionary, convert keys to a list

In [7]:

from datetime import datetime # For print_receipt

# Display all items in cart with prices and total
def display_cart(cart):
    i = 1
    for item in cart:
        print(f"{i}. {item} - ${cart[item]:.2f}")
        i += 1

# Add item to cart or update if exists
def add_to_cart(cart, item, price):
    cart[item] = price
    return cart

# Remove item by position number
def remove_from_cart(cart, item_number):
    i = 1
    for item in cart:
        if i == item_number:
            cart.pop(item)
            return cart
    print("WARNING: No item with number {i} found!")
    return cart


# Calculate total price of all items
def calculate_total(cart):
    total = 0
    for item in cart:
        total += cart[item]
    return total

# Helper function for nicely printing lines in receipt
def print_fill(left_side, right_side, filler, line_len):
    middle = ""
    while len(f"{left_side}{middle}{right_side}") < line_len:
        middle += filler
    print(f"{left_side}{middle}{right_side}")


def print_receipt(cart):
    print("========== RECEIPT =======")
    print(f"Date: {datetime.now().date().isoformat()}")
    print("")
    for item in cart:
        print_fill(item, f" ${cart[item]:.2f}", ".", 26)
    print("")
    subtotal = calculate_total(cart)
    tax = 0.08 * subtotal
    print_fill("Subtotal:", f" ${subtotal}", " ", 26)
    print_fill("Tax (8%):", f" ${tax:.2f}", " ", 26)
    print("--------------------------")
    total = subtotal + tax
    print_fill("Total:", f" ${total:.2f}", " ", 26)
    print("==========================")


# # Main program
cart = {}  # Empty dictionary to store items and prices
while True:
    print("Menu:")
    print("1. Display Cart")
    print("2. Add to Cart")
    print("3. Remove from Cart")
    print("4. Get Total")
    print("5. Checkout")
    choice = input("Enter choice: ")
    if choice == "1":
        display_cart(cart)
    elif choice == "2":
        item = input("Item: ")
        price = float(input("Price: "))
        cart = add_to_cart(cart, item, price)
    elif choice == "3":
        item_number = int(input("Item Number: "))
        cart = remove_from_cart(cart, item_number)
    elif choice == "4":
        total = calculate_total(cart)
        print(f"Total: {total:.2f}")
    elif choice == "5":
        print_receipt(cart)
        break
    else:
        print(f"Invalid option: {choice}")

Menu:
1. Display Cart
2. Add to Cart
3. Remove from Cart
4. Get Total
5. Checkout
Enter choice: 2
Item: Cheese
Price: 3.99
Menu:
1. Display Cart
2. Add to Cart
3. Remove from Cart
4. Get Total
5. Checkout
Enter choice: 2
Item: Milk
Price: 4.49
Menu:
1. Display Cart
2. Add to Cart
3. Remove from Cart
4. Get Total
5. Checkout
Enter choice: 2
Item: Eggs
Price: 14.89
Menu:
1. Display Cart
2. Add to Cart
3. Remove from Cart
4. Get Total
5. Checkout
Enter choice: 1
1. Cheese - $3.99
2. Milk - $4.49
3. Eggs - $14.89
Menu:
1. Display Cart
2. Add to Cart
3. Remove from Cart
4. Get Total
5. Checkout
Enter choice: 4
Total: 23.37
Menu:
1. Display Cart
2. Add to Cart
3. Remove from Cart
4. Get Total
5. Checkout
Enter choice: 5
========== RECEIPT =======
Date: 2025-08-01

Cheese.............. $3.99
Milk................ $4.49
Eggs............... $14.89

Subtotal:           $23.37
Tax (8%):           $18.70
--------------------------
Total:              $42.07
==========================

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