Skip to main content

Creating websites with Flask

What is Flask?​

Flask is a lightweight “micro” web framework for Python that makes building web applications straightforward with minimal boilerplate, offering simple routing via decorators, dynamic HTML templating with Jinja2, a built-in development server with interactive debugger, and an extensible ecosystem of optional extensions for tasks like database integration, form handling, and authentication; its unopinionated nature means you’re free to structure your project however you like, making Flask ideal for everything from small prototypes to full-scale, production-ready services.

Step 1. Install Flask​

Make sure you have Python 3.7+ installed.

In your project directory, create and activate a virtual environment:

python3 -m venv venv
source venv/bin/activate    # Linux/macOS
venv\Scripts\activate.bat   # Windows

Install Flask:

pip install Flask

Step 2: Create Your App File​

Create a file named app.py in your project directory with the following contents:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return '<h1>Hello, Flask on port 3000!</h1>'

if __name__ == '__main__':
    # Listen on all network interfaces, port 3000
    app.run(host='0.0.0.0', port=3000, debug=True)

  • host='0.0.0.0' Makes your server accessible from other machines on your network.

  • debug=True Enables auto-reload and more informative error messages during development.

Step 3: Run Your App​

From your project directory:

python app.py

You should see something like:

Open your browser to http://localhost:3000/ to see your “Hello, Flask” message.

Step 4: Next Steps​

  • Add More Routes
@app.route('/about')
def about():
    return '<h2>About Us</h2>'
  • Use Templates Create a templates/ folder and render HTML with Jinja2:
from flask import render_template

@app.route('/hello/<name>')
def hello(name):
    return render_template('hello.html', name=name)

  • Serve Static Files Put CSS, JavaScript, or images in a static/ folder.

  • Prepare for Production When ready to deploy, use a WSGI server (e.g., Gunicorn) and optionally front it with Nginx, still listening on port 3000 or proxying from 80/443.