Getting Started with Flask: Your First Python Web App

If you’ve been learning Python and want to build something you can show in a browser, Flask is the perfect starting point. Flask is a lightweight Python web framework that lets you go from zero to a working web app in minutes. In this guide, I’ll walk you through building your first Flask Python app step by step.

What Is Flask and Why Use It?

Flask is a “micro” web framework — it gives you just enough structure to build web apps without forcing you into a rigid pattern. Unlike Django, which comes with everything built in, Flask lets you add only what you need. That makes it ideal for beginners and small projects.

To install Flask, activate a virtual environment first, then run:

pip install flask

Building Your First Flask Route

A route in Flask maps a URL to a Python function. Create a file called app.py:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def home():
    return "<h1>Hello from Flask!</h1>"

if __name__ == "__main__":
    app.run(debug=True)

Run it with python app.py, open your browser to http://localhost:5000, and you’ll see your first Flask page. The debug=True flag means Flask will automatically reload when you save changes — very helpful while developing.

Rendering HTML Templates

Returning raw HTML strings from your functions gets messy fast. Flask has a built-in templating system called Jinja2. Create a templates/ folder and add index.html:

<!DOCTYPE html>
<html>
  <body>
    <h1>Hello, {{ name }}!</h1>
  </body>
</html>

Then update your route to use it:

from flask import Flask, render_template

app = Flask(__name__)

@app.route("/")
def home():
    return render_template("index.html", name="Kaikobud")

The {{ name }} in the template gets replaced with whatever you pass from Python. This separation of logic and presentation is a key web development concept.

Conclusion

Flask is one of the best ways to start building real web apps with Python. You’ve learned how to install it, define routes, and render HTML templates — that’s enough to build a personal homepage, a portfolio, or a simple tool. From here, explore adding forms, databases, and user authentication.

Read next: Building a REST API with Python and Flask — take your Flask knowledge further by building an API.

External resource: Flask Official Documentation — the best reference for everything Flask.

What Is Flask and Why Use It?

Building Your First Flask Route

Rendering HTML Templates

Conclusion

Kaikobud Sarkar

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