search

Introduction to sessions

A sessionarrow-up-right is used to store information related to a user, across different requests, as they interact with a web app. The data stored for a session should be considered temporary data, as the session will eventually expire. In order to permanently store date, you need to utilise a database.

Flask uses the client-side approach where sessions are stored in browser cookies. This cookie is sent with each request to the Flask app on the server-side where it's decoded.

Pros:

  • Validating and creating sessions is fast (no data storage)

  • Easy to scale (no need to replicate session data across web servers)

Cons:

  • Sensitive data cannot be stored in session data, as it's stored on the web browser

  • Session data is limited by the size of the cookie (usually 4 KB)

  • Sessions cannot be immediately revoked by the Flask app

from flask import Flask, request, redirect, session

app = Flask(__name__)
# SECRET_KEY is required to encrypt the contents of the session 
app.config['SECRET_KEY'] = 'This is a pretend secret key.' 

@app.route('/')
def home():
  # Access sessions values
  # Can also use `session['pet_name']` but it fails if the key isn't there.
  pet_name = session.get('pet_name', '')
  if pet_name:
    return f'<h1>Your pet\'s name is {pet_name}.</h1>'
  else:
    return f'<h1>I do not know your pet\'s name.</h1> <a href="/petname">set pet name</a>'

@app.route('/petname')
def pet_name():
  return f'<form method="POST"><input type="text" name="pet"><input type="submit"></form>'

@app.route('/petname', methods=['POST'])
def pet_name_action():
  pet_name = request.form.get('pet')
  # Set the session value
  session['pet_name'] = pet_name
  return redirect('/')

app.run(debug=True)

hashtag
Session Life

By default, the session object remains in place until the browser is closed. However, if you want to change the life of the session object, define the PERMANENT_SESSION_LIFETIMEarrow-up-right configuration variable after creating the Flask app:

When setting the data in the session, specify that the sessions should be permanent (time will be based on PERMANENT_SESSION_LIFETIME):

hashtag
References

PreviousDay 2: User sessions in FlaskNextHomework

Last updated