How to use FlaskSession in Python Flask (original) (raw)

Last Updated : 23 Jul, 2025

**Sessions in Flask store user-specific data across requests, like **login status, using cookies. Data is stored on the client side but signed with a secret key to ensure security. They help maintain user sessions without requiring constant authentication.

This article demonstrates how to implement **server-side sessions in Flask using the **Flask-Session extension. We’ll create a simple app that remembers a user’s name between requests, enabling login and logout functionality.

Installation

To learn how to create and set-up flask app, refer to- Create Flask App

After creating a Flask app, we need to install modules required in this project, to install them execute this command in the terminal-

pip install flask flask-session

File Structure

In the end, our file structure of the app should look similar to this

File Structure

Importing Modules and Configuring Flask-Session

In this section, we import the necessary modules and configure the Flask app to use server-side sessions. The configuration sets the session type (filesystem) and defines whether sessions are permanent.

Python `

from flask import Flask, render_template, redirect, request, session from flask_session import Session

app = Flask(name)

                # Configuration 

app.config["SESSION_PERMANENT"] = False # Sessions expire when the browser is closed app.config["SESSION_TYPE"] = "filesystem" # Store session data in files

Initialize Flask-Session

Session(app)

`

**Explanation:

• **Module Imports: Import Flask, its built-in session, and the Flask-Session extension.
• **Configuration:
  • **SESSION_PERMANENT is set to False so sessions expire when the browser closes.
  • **SESSION_TYPE is set to "filesystem" so that session data is stored on the server's disk.
• **Initialization: Calling Session(app) configures the Flask app to use the server-side session mechanism.

Defining Routes for Session Handling

Now we define the routes for the app that will handle the session. This application includes three routes- home route, login route and logout route:

Python `

@app.route("/") def index(): # If no username in session, redirect to login if not session.get("name"): return redirect("/login") return render_template("index.html")

@app.route("/login", methods=["GET", "POST"]) def login(): if request.method == "POST": # Record the user name in session session["name"] = request.form.get("name") return redirect("/") return render_template("login.html")

@app.route("/logout") def logout(): # Clear the username from session session["name"] = None return redirect("/")

`

**Explanation:

• **Home Route (/): Checks if the session contains a "name". If not, it redirects to the login page.
• **Login Route (/login): Displays a login form on **GET, on **POST, it stores the username from the form in the session and redirects to the home page.
• **Logout Route (/logout): Sets the session "name" to **None (or you could clear it) and redirects back to the home page.

HTML Files

Create the following html files in the templates folder:

layout.html

Provides a basic HTML structure and a block for inserting page-specific content.

HTML `

`

login.html

Contains a simple form to input a username. It extends layout.html.

HTML `

{% extends "layout.html" %}

{% block content %}

Register

`

index.html

Displays the current session's username (if available) and a logout link.

HTML `

{% extends "layout.html" %}

{% block content %} {% if session.name %} You are registered as {{ session.name }}. Logout. {% else %} You are not registered. Login. {% endif %} {% endblock %}

`

Complete app.py Code

Below is the complete code for **app.py:

Python `

from flask import Flask, render_template, redirect, request, session from flask_session import Session

app = Flask(name)

---------------- Configuration ----------------

app.config["SESSION_PERMANENT"] = False # Sessions expire when browser closes app.config["SESSION_TYPE"] = "filesystem" # Store session data on the filesystem Session(app)

---------------- Routes ----------------

@app.route("/") def index(): if not session.get("name"): return redirect("/login") return render_template("index.html")

@app.route("/login", methods=["GET", "POST"]) def login(): if request.method == "POST": session["name"] = request.form.get("name") return redirect("/") return render_template("login.html")

@app.route("/logout") def logout(): session["name"] = None return redirect("/")

if name == "main": app.run(debug=True)

`

When using Flask-Session with a filesystem backend, session data is stored on the server instead of in the browser. However, a session cookie (usually named session) is still sent to identify your session.

Let's see how we can view our session.

How to Check the Session

**Step 1: First start the application using this command in terminal-

python app.py

**Step 2: Register by entering a username to create a session, below is the snapshot of the live app

login.html

index.html

Step 3: After running the app and creatng a session, perform these steps-

1. **Open Developer Tools: Press F12 (or right-click → “Inspect”).
2. **Locate Cookies: In the Application (or Storage) tab, expand Cookies under your site’s domain to find the session cookie.

Below is the snapshot of a session.

Session