How cookies work in HTTP in Flask - Try It Yourself

How cookies work in HTTP with Flask

📖 Scenario: You are building a simple web app using Flask. You want to remember a visitor's name using cookies so that when they come back, the app greets them personally.

🎯 Goal: Create a Flask app that sets a cookie with the visitor's name and reads it back to greet them on return visits.

📋 What You'll Learn

Create a Flask app with one route '/'

Set a cookie named 'username' with value 'Alice' when the visitor first arrives

Read the 'username' cookie on subsequent visits

Display a greeting message using the cookie value if it exists

Use Flask's make_response to set cookies

💡 Why This Matters

🌍 Real World

Cookies are used by websites to remember users, keep them logged in, and personalize their experience.

💼 Career

Understanding cookies is essential for web developers to manage user sessions and preferences securely.

1

Set up the Flask app and route

Import Flask and request from flask. Create a Flask app called app. Define a route for '/' with a function called index that returns the string 'Welcome!'.

Flask

from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def index():
    # Your code here

Need a hint?

Start by importing Flask and request, then create the app and a simple route that returns a welcome message.

2

Add a variable to hold the cookie name

Create a variable called cookie_name and set it to the string 'username'.

Flask

from flask import Flask, request

app = Flask(__name__)

cookie_name = ''  # Your code here

@app.route('/')
def index():
    return 'Welcome!'

Need a hint?

This variable will store the name of the cookie we use to remember the visitor.

3

Check for the cookie and set it if missing

In the index function, import make_response from flask. Use request.cookies.get(cookie_name) to get the cookie value and store it in username. If username is None, create a response with the text 'Hello, new visitor!' and set a cookie named cookie_name with value 'Alice'. Otherwise, create a response with the text f'Welcome back, {username}!'. Return the response.

Flask

from flask import Flask, request, make_response

app = Flask(__name__)

cookie_name = 'username'

@app.route('/')
def index():
    # Your code here

Need a hint?

Use request.cookies.get() to read the cookie. Use make_response() to create a response and set_cookie() to add a cookie.

4

Add the app run command

Add the standard Flask app run block: if __name__ == '__main__': and inside it call app.run(debug=True).

Flask

from flask import Flask, request, make_response

app = Flask(__name__)

cookie_name = 'username'

@app.route('/')
def index():
    username = request.cookies.get(cookie_name)
    if username is None:
        response = make_response('Hello, new visitor!')
        response.set_cookie(cookie_name, 'Alice')
    else:
        response = make_response(f'Welcome back, {username}!')
    return response

# Your code here

Need a hint?

This block runs the Flask app when you start the script.