[Python] Flask : Storing , Get and Update List in session using flask_session

I have been trying for a couple of days, but I have had no success using a session to store the list( e.g., list of notes).

Below is the code that I have written. It store 2 variables successfully and when I try adding the third variable to the list , it overrides the second variable instead of appending to the list

from flask import Flask, render_template, request, session
from flask_session import Session

app = Flask(__name__)

app.config['SECRET_KEY'] = "some_random"
app.config['SESSION_TYPE'] = 'filesystem'
app.config['SESSION_PERMANENT']= False

Session(app)

@app.route("/notes", methods=["GET","POST"])
def addNotes():
if 'notes' not in session:
session['notes'] = []
if request.method == "POST":
note=request.form.get("note")
notes_list = session['notes']
notes_list.append(note)
session['notes'] = notes_list


return render_template("notes.html", notes=session['notes'])


notes.html :

{% extends "layout.html" %}

{% block heading %}
Sticky Notes
{% endblock %}

{% block body %}

<ul>
{% for note in notes %}
<li>{{ note }}</li>
{% endfor %}
</ul>

<form action="{{ url_for('addNotes') }}" method="POST">
<input type="text" name="note" placeholder="Enter a note here">
<button>Add Note</button>
</form>
{% endblock %}


Please suggest if there is any way to store, get and update the list variable stored in the session object.

I have tried using session.modification=True also, which was based on some suggestions on stackoverflow.

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