Python Project: Building a Store Calculator

Introduction:

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I created a Store Calculator using Python. It is a simple program that calculates the total amount of items, allows the user to quit by pressing "q," and generates a receipt with all item prices. In this article, I’ll share how I built this calculator, the challenges I faced, and their solutions.

These are the steps I took to grasp the concepts:

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1. The first step is to understand the below objective:

   • Accept item prices as input.

   • Allow quitting by pressing "q."

   • Generate a receipt with items and the total price.

2. Writing the Code:

   • Used a while loop to get inputs until the user quits.

   • Stored prices and calculated the total.

   • Displayed a receipt at the end.

3. Error Handling:

   • Checked for invalid inputs (e.g., letters other than "q" or empty values).

   • Prevented negative prices from being entered.

4. Below is the full code snippet :

These are the problems that I encountered:

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1. Validating User Input to Avoid Crashes.

2. Negative Price Handling Error.

3. Misplacement of break Statement.

This is how I solved those problems:

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1. Validating User Input to Avoid Crashes:

Problem**:** The program would crash if the user entered something other than a number or "q."

userinput = input("Enter the item price or press q to quit: ")
# If the input is not a valid number or "q", the program would crash.

Solution: Added try-except block to catch invalid inputs and prompt the user correctly.

try:
    price = float(userinput)  # Try to convert the input to a number
except ValueError:
    print("Invalid input. Please enter a valid number or 'q' to quit.")

2. Negative Price Handling Error:

Problem: The program accepted negative prices, which doesn’t make sense for the store calculator.

price = float(userinput)
# No validation for negative price.

Solution: Added a check to ensure only positive numbers are accepted.

if price < 0:
    print("Invalid input. Please enter a positive number.")

3. Misplacement of break Statement:

Problem**:** The break statement was placed inside the loop after every valid input, causing the program to exit prematurely.

if userinput.lower() == "q":
    print("\nReceipt Generated:")
    break  # Incorrect placement of break

Solution: Moved the break statement to only activate when the user presses "q" and the receipt is ready.

if userinput.lower() == "q":
    print("\nReceipt Generated:")
    for i, price in enumerate(prices, start=1):
        print(f"Item {i}: {price}")
    print(f"\nTotal: {sum:.2f}")
    break  # Correct placement to exit after generating receipt

Output when running in the terminal:

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Enter the item price or press 'q' to quit: 25
The total price so far: 25.0.
Enter the item price or press 'q' to quit: 
Invalid input. Please enter a valid number or 'q' to quit.
Enter the item price or press 'q' to quit: -95
Invalid input. Please enter a positive number or 'q' to quit.
Enter the item price or press 'q' to quit: 95
The total price so far: 120.0.
Enter the item price or press 'q' to quit: 40
The total price so far: 160.0.
Enter the item price or press 'q' to quit: P
Invalid input. Please enter a valid number or 'q' to quit.
Enter the item price or press 'q' to quit: q

Receipt Generated:
Item 1: 25.0
Item 2: 95.0
Item 3: 40.0

The total price is 160.0. Thanks for shopping.

Resources:

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My GitHub repository with the project code: GitHub Link