Flask Session & Cookies

1. Setting Up Flask

Step 1: Install Flask and Create a Basic App

pip install flask
mkdir flask_session_cookies
cd flask_session_cookies

Create app.py and add the basic Flask setup:

from flask import Flask, render_template, request, redirect, url_for, session, make_response

app = Flask(__name__)
app.secret_key = 'your_secret_key'  # Required for session handling

@app.route("/")
def home():
    return render_template("index.html")

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

2. Handling Cookies in Flask

Step 2: Setting and Getting Cookies

Modify app.py to add routes for setting and retrieving cookies:

@app.route("/set_cookie")
def set_cookie():
    response = make_response("Cookie has been set!")
    response.set_cookie("username", "FlaskUser", max_age=60*60*24)  # Expires in 1 day
    return response

@app.route("/get_cookie")
def get_cookie():
    username = request.cookies.get("username")
    return f"Stored Cookie: {username}" if username else "No cookie found!"

Step 3: Deleting a Cookie

@app.route("/delete_cookie")
def delete_cookie():
    response = make_response("Cookie deleted!")
    response.set_cookie("username", "", expires=0)
    return response

3. Using Sessions in Flask

Step 4: Setting and Retrieving Session Data

Modify app.py to store user data in a session:

@app.route("/set_session")
def set_session():
    session["user"] = "JohnDoe"
    return "Session set for user!"

@app.route("/get_session")
def get_session():
    user = session.get("user")
    return f"Stored Session: {user}" if user else "No session found!"

Step 5: Deleting a Session

@app.route("/delete_session")
def delete_session():
    session.pop("user", None)
    return "Session data cleared!"

4. Creating a Simple Login System Using Sessions

Step 6: Create a Login Form

Inside the templates folder, create index.html:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Flask Sessions & Cookies</title>
</head>
<body>
    <h1>Flask Session & Cookies Example</h1>
    
    <form action="/login" method="POST">
        <label>Username:</label>
        <input type="text" name="username" required>
        <button type="submit">Login</button>
    </form>

    <p><a href="/logout">Logout</a></p>
</body>
</html>

Step 7: Add Login and Logout Routes

Modify app.py to handle user login using sessions:

@app.route("/login", methods=["POST"])
def login():
    session["user"] = request.form["username"]
    return redirect(url_for("dashboard"))

@app.route("/dashboard")
def dashboard():
    if "user" in session:
        return f"Welcome {session['user']}! <br><a href='/logout'>Logout</a>"
    else:
        return redirect(url_for("home"))

@app.route("/logout")
def logout():
    session.pop("user", None)
    return redirect(url_for("home"))

5. Running the Flask App

Step 8: Start the Flask Server

python app.py

Open http://127.0.0.1:5000/, enter a username, and click Login.

If successful, you’ll see a dashboard with a Logout option.
Clicking Logout clears the session and redirects back to the homepage.

Conclusion

In this guide, you learned how to:

✅ Use cookies to store small data on the client-side
✅ Use sessions to store user data securely on the server
✅ Build a simple login/logout system with sessions

Now, you can manage user authentication and stateful data in your Flask applications! 🚀

PYTHON FLASK