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Walkthrough: Terminal Hello Lab

This guide walks through the thinking process for building this project. It does NOT give you the complete solution. For that, see SOLUTION.md.

Before reading this

Try the project yourself first. Spend at least 20 minutes. If you have not tried yet, close this file and open the project README.

Understanding the problem

You need to build a script that asks the user for their name and which day of their Python journey it is, then prints a decorated banner, a personalised greeting, a fun fact, and an info card. The key functions are greet(), build_banner(), build_info_card(), and run_hello_lab().

This is your first project with tests. The functions must return values (not just print), so the tests can call them directly and check the output.

Planning before code

flowchart TD
    A[User types name and day] --> B[greet: build greeting string]
    A --> C[build_banner: create bordered title]
    B --> D[run_hello_lab: print everything]
    C --> D
    D --> E[build_info_card: collect summary dict]
    E --> F[Print info card]

Break the project into three independent building blocks, then one function that ties them together:

  1. greet() -- take a name, return a greeting string
  2. build_banner() -- take a title, return a bordered banner
  3. build_info_card() -- take name/language/day, return a dictionary
  4. run_hello_lab() -- call the above, print everything, return the info card

Step 1: The greeting function

Start with the simplest piece. greet() takes a name and returns a string.

def greet(name: str) -> str:
    return f"Hello, {name}! Welcome to Python."

The f-string f"Hello, {name}!" inserts the value of name into the text. This is cleaner than concatenation ("Hello, " + name + "!").

Predict before you scroll

What does greet("Ada") return? What about greet("")? Is an empty-name greeting a problem the tests will care about?

Step 2: The banner function

The banner wraps a title in asterisks. You need: - A top border (a line of * characters) - The title, centred - A bottom border

def build_banner(title: str, width: int = 40) -> str:
    border = "*" * width
    centered_title = title.center(width)
    return f"{border}\n{centered_title}\n{border}"

Two things to notice: - "*" * width repeats the * character width times. This is string multiplication. - .center(width) pads the string with spaces on both sides so it sits in the middle.

Predict before you scroll

If width is 40 and title is "HI", how many spaces will appear before "HI" in the centred line?

Step 3: The info card

This function collects facts into a dictionary. Dictionaries let you label data with keys instead of relying on position.

def build_info_card(name: str, language: str, day: int) -> dict:
    return {
        "name": name,
        "language": language,
        "learning_day": day,
        "greeting": greet(name),  # reuses greet()!
    }

Notice that build_info_card calls greet() inside it. Functions can call other functions -- this is composition.

Step 4: Tying it together

run_hello_lab() is the orchestrator. It calls the building blocks, prints output, and returns the info card.

def run_hello_lab(name: str, day: int) -> dict:
    print(build_banner("TERMINAL HELLO LAB"))
    print()
    print(greet(name))
    print(f"\tDay {day} of your Python journey.")
    # ...
    return build_info_card(name, "Python", day)

The \t inside the f-string is a tab character -- it indents the text.

Common mistakes

Mistake Why it happens How to fix
greet() prints instead of returning Confusing print() with return print() shows text on screen; return sends data back to the caller. Tests need return.
Banner width is wrong Forgetting that .center() pads to a total width, not adds that much padding .center(40) makes the whole string 40 characters wide
int(input(...)) crashes on non-numbers The user typed letters instead of a number Wrap in try/except ValueError or check .isdigit() first
Forgetting if __name__ == "__main__" Not understanding the guard Without it, the input() calls run when tests import the file

Testing your solution

Run the tests from the project directory:

pytest -q

The five tests check: - greet("Ada") contains "Ada" and "Hello" - greet() works for multiple different names - build_banner("MY TITLE") contains the title and has 3 lines - build_banner("HI", width=20) produces borders exactly 20 characters wide - build_info_card("Test", "Python", 5) returns a dict with all expected keys

If a test fails, read the assertion error carefully -- it tells you what value it expected vs. what it got.

What to explore next

  1. Add a build_greeting_box() function that wraps the greeting in a box made of +, -, and | characters
  2. Add input validation: what should happen if the user types nothing for their name, or letters for the day number?