Session - a dictionary object containing session variables and associated values.

session.pop()
secret_key

vi session.py

from flask import Flask, session, redirect, url_for, escape, request
ap = Flask(__name__)

@ap.route('/sessions')
def sessions():
   if 'username' in session:
      username = session['username']
      return 'Logged in as ' + username + '<br>' + \
         "<b><a href = '/logout'>click here to log out</a></b>"
   return "You are not logged in <br><a href = '/login'></b>" + \
      "click here to log in</b></a>"

@ap.route('/login', methods = ['GET', 'POST'])
def login():
   if request.method == 'POST':
      session['username'] = request.form['username']
      return redirect(url_for('sessions'))
   return \[code\]'

   <form action = "" method = "POST">
      <p><input type = "text" name = "username"/></p>
      <p<<input type = "submit" value = "Login"/></p>
   </form>
   
   \[/code\]'
     
@ap.route('/logout')
def logout():
   # remove the username from the session if it is there
   session.pop('username', None)
   return redirect(url_for('sessions'))

ap.secret_key = '<any random string>'

if __name__ == '__main__':
   ap.run(host= '0.0.0.0')
==

https://www.jjude.com/flask-errors/