How to retrieve session data with Flask?

Question

I have flask+wtforms application. I can see in login() user object stored as

  if user:
   if user.verify_password(form.password.data):
    flash('You have been logged in')
    user.logins += 1

    db.session.add(History(user.uid))
    db.session.commit()

    session['user'] = user

Now I wanted to retrieve the user

if 'user' in session:
       User=session.get('user')
       print User.nickname ###<< how to retrieve specific object member?

It fails with message like :

Instance <User at 0x8e5a64c> is not bound to a Session; attribute refresh operation cannot proceed

Jacquline

Answer 1

It's simple. If you want to retrieve a specific object simply add the name of the variable within session, e.g. session['nickname'].

You can set the variable the same way, by doing session['nickname'] = nickname.

In your case you would change it to the following

if 'user' in session:
    user = session['user']
    print user

if 'nickname' in session:
    nickname = session['nickname']
    print nickname

This is an simplified version of the function I use for login.

@app.route('/login', methods=['POST'])
def login():
    """Authenticate User"""
    username = request.form['username'].strip()
    nickname = request.form['nickname'].strip()
    password = request.form['password']
    try:
        if Auth().VerifyLogin(username, password):
            session['username'] = username
            session['nickname'] = nickname
        else:
            # failed to login, do something.
    except Exception as why:
        app.logger.critical('.....')

Giltzow

How to retrieve ,if its an object? Please check above edit code part. 'user' is an object which has members like user.uid,user.logins and user.nickname – Jacquline

Thanks a lot,got it. Used your first method. Not worrying about objects and things like that. Stored the nickname as session variable rather than object. Thanks for the help. – Jacquline

No worries. btw for security reasons it's best to store the least amount of information in the session possible. I store all my permissions etc in a database. – Giltzow

the app uses mysql, I don't have much data stored session. Just now trying to re-use session..in order to add a new user-edit profile page in the website. – Jacquline

Note also that session cookies have a size limit of 4kb - over that and the session gets blanked, which can cause some confusing bugs! – Schapira

Answer 2

To see all that is in your session you can print(session). You should get a response like

<SecureCookieSession {'_flashes': [('info', 'Duplication is not allowed ')], 'el1-s': 'Physics', 'el1grade-s': 'B2', 'el2-s': 'E-Maths', 'el2grade-s': 'A1', 'english-s': 'A1', 'mathematics-s': 'A1', 'science-s': 'A1', 'social-s': None}>

Kanpur