将flask会话变量传递到其他视图将返回类型None

Question

I am trying to pass a session variable that is set on the login view, to another view. However, the session variable always returns None if a form is submitted, I want the session variable to retain.

The tools page has some form fields, and one text box that handles autocomplete search based off of the session['foo'] which is sent on good login.

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        # Get some form variables here
        if login is valid:
            login_user(user, remember=True)
            session['foo'] = utils.get_data()
            return redirect(url_for('tools'))
    return render_template('login.html')

@app.route("/tools", methods=['GET', 'POST'])
@login_required
def tools():
    if session['foo'] is None:
        print "Data is None type, getting data"
        session['foo'] = utils.get_data()

    if request.method == 'POST':
        # Handling some forms here
        # If one of these forms are submitted, session['foo'] is set to None :(

    return render_template('tools.html', foo_data=session['foo'])

Utils.py

def get_data():
    response = requests.post(url, data=data)  # FYI, server won't allow GET for this call.
    # Do json type stuff here to make response.content nice for javascript
   return response

Essentially, what happens with this code is, every time I submit a form, I have to check if it's None and invoke utils.get_data(), I want the data returned by this method to retain for the entire length of the session.

EDIT: Solution, session variable object is too big. Some ways to solve this could include;

• Use AJAX to avoid refresh the page each submission, thus not flushing the session object
• Split the object into smaller chunks
• Avoid storing large objects in cookies- use local storage

Answer 1

Check the size of the data being put into session. And if it is too large try using a smaller object.

From the documentation

A note on cookie-based sessions: Flask will take the values you put into the session object and serialize them into a cookie. If you are finding some values do not persist across requests, cookies are indeed enabled, and you are not getting a clear error message, check the size of the cookie in your page responses compared to the size supported by web browsers.

Original post:

Technically the utils.get_data method is a separate session than the web call. What is the get data method trying to achieve?

Answer 2

You can also create a server-side session if the data size is the problem. It is possible to store Flask sessions inside your database and just store the session id in the cookie.

For example this snippet shows how to store your session data in MongoDB.