How to use Flask-Session in Python Flask ?

Flask Session – 

• Flask-Session is an extension for Flask that supports Server-side Session to your application.
• The Session is the time between the client logs in to the server and logs out of the server.
• The data that is required to be saved in the Session is stored in a temporary directory on the server.
• The data in the Session is stored on the top of cookies and signed by the server cryptographically.
• Each client will have their own session where their own data will be stored in their session.

Uses of Session

• Remember each user when they log in
• Store User-specific website settings (theme)
• Store E-Commerce site user items in the cart

This article assumes you are familiar with flask basics. Checkout – Flask – (Creating first simple application) to learn how to make a simple web application in flask.

Installation

Install the extension with the following command

$ easy_install Flask-Session

Alternatively, if you have pip installed

$ pip install Flask-Session

Configuring  Session  in  Flask

• The Session instance is not used for direct access. You should always use flask_session.
• The First line (session) from the flask is in such a way that each of us as a user gets our own version of the session.

Python3

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

This is specific to the flask_session library only

• SESSION_PERMANENT = False –  So this session has a default time limit of some number of minutes or hours or days after which it will expire.
• SESSION_TYPE = “filesystem” –   It will store in the hard drive (these files are stored under a /flask_session folder in your config directory.) or any online ide account, and it is an alternative to using a Database or something else like that.

Python3

app = Flask(__name__)
app.config["SESSION_PERMANENT"] = False
app.config["SESSION_TYPE"] = "filesystem"
Session(app)

Remember User After Login

So we will start making two basic pages and their route called index.html and login.html

• login.html contains a form in which the user can fill their name and submit 
• index.html is the main page 

Python3

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


@app.route("/login", methods=["POST", "GET"])
def login():
    return render_template("login.html")

• We need to record the username in the session when they submit the form
• And we are using a dictionary in python where “name” is the key = request.form.get(“name”) is a value

Python3

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

• After storing the user name we need to check whenever user lands on the index page that any session with that user name exists or not.
• If the user name doesn’t exist then redirect to the login page.

Python3

@app.route("/")
def index():
  # check if the users exist or not
    if not session.get("name"):
        # if not there in the session then redirect to the login page
        return redirect("/login")
    return render_template('index.html')

• After successfully remember the user we also need a way to logout the users.
• So whenever the user clicks logout change the user value to none and redirect them to the index page.

Python3

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

Complete Project –

Python3

from flask import Flask, render_template, redirect, request, session
# The Session instance is not used for direct access, you should always use flask.session
from flask_session import Session

app = Flask(__name__)
app.config["SESSION_PERMANENT"] = False
app.config["SESSION_TYPE"] = "filesystem"
Session(app)


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


@app.route("/login", methods=["POST", "GET"])
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)

index.html

• We can also use session.name to excess the value from the session.

HTML

{% extends "layout.html" %}

{% block y %}

   {% if session.name %}
      You are Register {{ session.name }} <a href="/logout">logout</a>.
   {% else %}
      You are not Register. <a href="/login">login</a>.
   {% endif %}

{% endblock %}

login.html

HTML

{% extends "layout.html" %}

{% block y %}

   <h1> REGISTER </h1>

   <form action="/login" method="POST">
      <input placeholder="Name" autocomplete="off" type="text" name="name">
      <input type="submit" name="Register">
   </form>

{% endblock %}

layout.html

HTML

<!DOCTYPE html>

<html lang="en">
    <head>
        <meta name="viewport" content="initial-scale=1, width=device-width">
        <title> flask </title>
    </head>
    <body>
        {% block y %}{% endblock %}
    </body>
</html>

Output – 

login.html

index.html

You can also see your  generated  session.