Check Yourself
Before you submit, make sure you can answer these questions. If you're stuck on any of them, go back and reread the relevant page.
Conceptual
What's the difference between flask (lowercase) and Flask (uppercase)?
flask is the Python library (the LEGO collection). Flask is the class inside that library (the specific box that builds the main robot). from flask import Flask pulls the class out of the library.
Why does the function use return instead of print?
return sends data back through Flask to the browser — it becomes the web page. print() writes to the terminal only. The browser never sees print() output.
What does the @ decorator do?
It turns the function below it into a trigger. Instead of running top-to-bottom, the function runs only when Flask receives an HTTP request matching the route path. It's like an event handler.
What happens when you visit a URL that doesn't match any route?
Flask returns a 404 Not Found error. It checked every @app.route and none matched the requested path.
Why do we move HTML into separate files instead of keeping it in Python strings?
Separation of concerns. Python handles the logic (which function runs for which URL). HTML handles the presentation (what the page looks like). Keeping them in separate files means you get proper syntax highlighting for both, and neither file becomes unreadable.
Practical
- Run
flask run --debugand see the app in a browser? - Add a new route and see it appear without restarting?
- Use a route variable to capture part of the URL?
- Add
<a href>links between your pages? - Create an HTML file in
templates/and serve it withrender_template()? - Add an image to
static/and display it with<img src="/static/...">? - Stop the server with
Ctrl+Cand start it again?
@app.route("/greet/<name>")
def greet(name):
return f"<h1>Hello, {name}!</h1>"What URL would you visit to see "Hello, Alice!"?
Answer
/greet/Alice — Flask extracts Alice from the URL, passes it to the name parameter, and the f-string puts it in the heading.
What's next
Your app has routes, HTML files in templates/, and render_template() serving them. But every page is still static — the same HTML every time, for every visitor.
Week 2 introduces Jinja2 — a way to put placeholders in your HTML files that Flask fills in with Python data. You'll also learn base.html and template inheritance, so your nav bar and footer live in one place instead of being copy-pasted across every page.