Built-In Functions and print()
Learn Python’s built-in functions and the print() function by building your first digital receipt.
The project
You’ve probably gone shopping more times than you can count. You walk into the store, choose what you need, bring everything to the counter, and watch as the cashier scans each item. The prices appear on the screen, and finally, the receipt prints. That receipt isn’t random; it’s produced by a program that tells the system exactly what to show and in what order. This type of program is known as a point-of-sale (POS) system.
In this lesson, we’ll create our own small version of that system. No calculations yet, no storing of data, just printing the receipt text exactly as it should appear on the screen.
This is what the receipt looks like:
You have been hired to create this POS system! But here’s the twist, for now, we’ll create this receipt exactly as shown. Our only tool will be Python’s built-in print() function.
The programming concept
The concept for today is built-in functions, special commands that Python already knows. You don’t have to invent them; you just use them.
The one we’ll start with is print(). Its job is simple: show text or numbers on the screen. You put the thing you want to display inside the parentheses, and Python will show it to you.
Example:
print("Hello World")
Click the “Run” button to check the output of this code.
Congratulations. You are officially a programmer. This is an age-old tradition in the programming community: start learning a new programming language by printing “Hello, World” on the screen!
The significance of the concept in the project
If you look closely at our receipt, it’s just lines of text and numbers. Without print(), nothing would appear on the screen. For this first version of our point-of-sale app, each line of the receipt will be produced by a separate print() statement.
Concept at a glance:
print() is a built-in function. It tells Python to show something on screen.
The thing you want to show must go inside parentheses, like this: print(...)
If it’s text, you must put it in quotes: "Hello!"
Learn to code the concept
Let’s try printing the first two lines of our receipt:
print("=== MART RECEIPT ===")print("Cashier Name: Alex")
Run this and you’ll see:
=== MART RECEIPT ===Cashier Name: Alex
To match the full receipt, we just keep adding more print() statements for each line.
Learn to code with AI
If you’re working with an AI assistant, you can simply tell it:
Prompt:
Write a Python program that prints this exact receipt using only print() statements:=== MART RECEIPT ===Cashier Name: AlexItems Purchased:Milk (1): 4Bread (1): 2Eggs (12): 0.5 x 12 = 6Total bill: 4 + 2 + 6 = 12
The AI will give you working code immediately, ready to run.
Generate code with AI
Here is the Copilot, where you can write your prompt and get it to generate code for you.
Test code with AI
Once the AI has generated the code, copy-paste it into the following code widget, run it, ask the “AI Mentor” for feedback, and
# Write your code for receipt generation
Food for thought:
What happens if you try to print some text without quotes, e.g., print(Hello)?
What happens if you try to print some text without parentheses, e.g., print Hello?
If it’s text, you must put it in quotes: “Hello!”
Practice makes perfect
Wonderful. You’ve managed to execute a successful Python program that meets your client’s requirements. But the code was generated by AI, let’s see if you’ve learnt to simple enough concept. You have to use the concept you’ve learnt to solve a similar problem.
Problem
Print the following receipt exactly as shown, using only print() statements:
=== MART RECEIPT ===Cashier Name: SamItems Purchased:Pen (1): 20Notebook (1): 45Bag (1): 120Total bill: 20 + 45 + 120 = 185
Code its solution
The final output should match the sample output shown above:
# Write your code for reciept generation
Perfect! Now your POS app has successfully launched and is ready to ship to customers.