Flask session variable not persisting between requests

Question

Using the app below and Flask 0.11.1, I navigated to the routes associated with the following function calls, with the given results:

• create(): \'1,2,3\'

Answer 1

From the doc:

Be advised that modifications on mutable structures are not picked up automatically, in that situation you have to explicitly set the [modified attribute] to True yourself.

Try:

session['list'].remove(str(id))
session.modified = True

Answer 2

Flask uses a CallbackDict to track modifications to sessions.

It will only register modifications when you set or delete a key. Here, you modify the values in place, which it will not detect. Try this:

@app.route('/r/<int:id>')
def remove(id):
    val = session['list']
    val.remove(str(id))
    session['list'] = val
    return ",".join(session['list'])

…and same with other changes.

Alternatively, you can flag the modification yourself instead of triggering the detection:

@app.route('/r/<int:id>')
def remove(id):
    session['list'].remove(str(id))
    session.modified = True
    return ",".join(session['list'])