🔧 Lab 05 — Write and Run Real Python

Time: 60–90 minutes. Tools: a web browser — laptop is comfiest, but a phone works. Nothing to install. Free.

Today you run real code. Five exercises, each building on the last. Type the code yourself rather than copy-pasting — your fingers learn faster than your eyes.

Step 0: Open a Python playground (5 min)

You need a website where you can type Python and press Run. Any of these works — pick the first one that loads for you:

trinket.io — go to the site and look for an option to try or create a Python trinket without an account. You’ll get two panels: one to type code in, one showing the output, with a Run button (often a “play” ▶ triangle).
The official Python console at python.org/shell — a black box where you type one line, press Enter, and see the result immediately. Fine for Exercise 1, but for the later exercises (which have many lines) a two-panel site like trinket is more comfortable.
Fallback: search the web for “run Python online free”. Many good sites exist (look for names like Replit or Programiz). You want: a place to type multiple lines, and a Run button. Avoid anything demanding payment; sign-up should not be required — if a site insists on one, try another.

⚠️ Watch out: websites redesign their buttons regularly, so don’t worry if yours doesn’t match these descriptions word for word. Whatever the site looks like, you are looking for exactly two things: a box to type code in and a Run button. Find those and you’re in business.

✅ What you should see: an empty code area, ready for you. That blank box is the same blank box every programmer on Earth started with.

Exercise 1: Hello, world (5 min)

In the code area, type exactly (capitals, brackets, and quotes matter):
```
print("Hello, world!")
```
Press Run.

✅ What you should see:

Hello, world!

Now make it yours. Change the message to greet you by name, and add a second print line below it saying anything you like. Run again.

✅ What you should see: your two messages, in order, top to bottom. Programs run top to bottom — you’ve now proven it.

Exercise 2: Mad-libs with variables (10 min)

Variables are labeled jars. Let’s fill some and build a silly sentence.

Clear the code area (or start a new file) and type:

name = "Zork"
animal = "hedgehog"
number = 17
print(name + " owns " + str(number) + " " + animal + "s.")

Press Run.

✅ What you should see:

Zork owns 17 hedgehogs.

Now change only the first three lines — new name, new animal, new number — and run again. The sentence updates without touching the print line. That’s the point of variables: the sentence is a template; the jars hold the changeable parts.
Notice the str(number) in line 4. Try removing str( and its matching ) so it reads ... + number + ..., and run.

✅ What you should see: an error mentioning something like can only concatenate str (not "int") to str. Translation from proofreader-speak: “you asked me to glue text to a number, and I only glue text to text.” Put the str(...) back — it converts the number into text first. Congratulations: that was your first deliberate error, and you read the message. That’s the habit.

Exercise 3: The age gate (10 min)

The bouncer from the lesson, live.

New program:

age = int(input("How old are you? "))
if age >= 18:
    print("Come on in!")
else:
    print("Sorry, adults only.")

Careful with the details: the lines under if and else are indented (pushed right — use 4 spaces or the Tab key), and both if and else lines end with a colon :.
Run it. The program will wait for you — type an age into the output panel and press Enter.

✅ What you should see: with 25, you get Come on in!. Run again with 12: Sorry, adults only. Same program, different path — that’s the fork in the road.

Stretch goal: add an elif age >= 16: branch between the if and the else that prints something like "You may enter with a guardian." Run all three cases: 25, 16, 12.

Exercise 4: Countdown (10 min)

New program:

countdown = 5
while countdown > 0:
    print(countdown)
    countdown = countdown - 1
print("Lift off! 🚀")

Note which lines are indented: the two lines under while are inside the loop; the final print is not indented, so it runs after the loop finishes.
Run it.

✅ What you should see:

5
4
3
2
1
Lift off! 🚀

Experiment time: change the starting number to 10. Then try changing countdown - 1 to countdown - 2 — before running, predict what will print. Were you right?

⚠️ Watch out: if you ever remove the countdown = countdown - 1 line, the loop becomes infinite — it will print the same number forever. This is a rite of passage, and it’s harmless: every playground has a Stop button (often where Run was). Press it, fix the code, carry on. You are now officially someone who has survived an infinite loop.

Exercise 5: Mini-project — the Compliment Machine (20 min)

Your first program designed by you. Specification: the program asks for the user’s name and their mood, then responds with a compliment that uses both answers.

Start from this skeleton and finish it:

print("Welcome to the Compliment Machine!")
name = input("What's your name? ")
mood = input("How are you feeling today? ")

Add lines so the machine responds. Minimum version: one print that weaves name into a compliment.
Better version: use if / elif / else on the mood answer. For example: if mood == "sad": print something extra kind; elif mood == "happy": print something celebratory; else: a general-purpose compliment. (Note the double equals == — it means “is equal to?”, a question — while single = means “store this in the jar.” Mixing them up is a classic; the proofreader will tell you.)
Deluxe version: end with a for loop that showers them with three compliments from a list — flip back to the lesson’s for example for the shape of it.

✅ What you should see (your wording will differ — that’s the point):

Welcome to the Compliment Machine!
What's your name? Maria
How are you feeling today? sad
Maria, anyone would be lucky to know you.
Chin up — bad days are outnumbered by good ones.

If it runs and responds using both answers: you have written your first real program from a specification. That’s not a beginner’s imitation of the job. That is the job.

🩹 When you get an error (read this the moment you need it)

You will hit errors in this lab. Everyone does; it is part of the plan, not a deviation from it. When it happens:

Breathe. Nothing is broken. Your code is saved. The computer is not upset.
Read the last line of the message — it names the problem (SyntaxError: '(' was never closed, NameError: name 'nme' is not defined…).
Find the line number in the message and look at that line — and the line above it (a missing bracket on line 3 is often reported on line 4).
Check the usual suspects: a missing closing bracket ), a missing quote ", a missing colon : after if/else/while/for, indentation that doesn’t match, or a variable name spelled two different ways.
Fix one thing, run again. The proofreader complains about one problem at a time; that’s normal.

Still stuck after five minutes? Retype the example from the lab exactly, confirm it runs, then re-make your changes one at a time, running after each. The step that breaks it is the bug — and now you know where it lives.

Done?

Save or copy your Compliment Machine somewhere — it’s the first entry in your portfolio. Then take the quiz, browse the resources, and when you’re ready, on to Module 06 — Data.