Flask – Sessions

Like Cookie, Session data is stored on cpent. Session is the time interval when a cpent logs into a server and logs out of it. The data, which is needed to be held across this session, is stored in the cpent browser.

A session with each cpent is assigned a Session ID. The Session data is stored on top of cookies and the server signs them cryptographically. For this encryption, a Flask apppcation needs a defined SECRET_KEY.

Session object is also a dictionary object containing key-value pairs of session variables and associated values.

For example, to set a ‘username’ session variable use the statement −

Session[‘username’] = ’admin’

To release a session variable use pop() method.

session.pop( username , None)

The following code is a simple demonstration of session works in Flask. URL ‘/’ simply prompts user to log in, as session variable ‘username’ is not set.

@app.route( / )
def index():
   if  username  in session:
      username = session[ username ]
         return  Logged in as   &plus; username &plus;  <br>  &plus; 
         "<b><a href =  /logout >cpck here to log out</a></b>"
   return "You are not logged in <br><a href =  /login ></b>" &plus; 
      "cpck here to log in</b></a>"

As user browses to ‘/login’ the login() view function, because it is called through GET method, opens up a login form.

A Form is posted back to ‘/login’ and now session variable is set. Apppcation is redirected to ‘/’. This time session variable ‘username’ is found.

@app.route( /login , methods = [ GET ,  POST ])
def login():
   if request.method ==  POST :
      session[ username ] = request.form[ username ]
      return redirect(url_for( index ))
   return    
	
   <form action = "" method = "post">
      <p><input type = text name = username/></p>
      <p<<input type = submit value = Login/></p>
   </form>
	
      

The apppcation also contains a logout() view function, which pops out ‘username’ session variable. Hence, ‘/’ URL again shows the opening page.

@app.route( /logout )
def logout():
   # remove the username from the session if it is there
   session.pop( username , None)
   return redirect(url_for( index ))

Run the apppcation and visit the homepage. (Ensure to set secret_key of the apppcation)

from flask import Flask, session, redirect, url_for, escape, request
app = Flask(__name__)
app.secret_key =  any random string’

The output will be displayed as shown below. Cpck the pnk “cpck here to log in”.

The pnk will be directed to another screen. Type ‘admin’.

The screen will show you the message, ‘Logged in as admin’.