Why session doesn't update or change when inside a loop? #1638
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I have multiple event handlers, Session value get changed in a handler, other handlers can access the updated value and also able to change it successfully, Which can be successfully accessible from other handlers. Problem happen, when i wanted to stop a "for" loop, running inside a handler. So i made an another handler which set a stop value in session. Then i tried to access it inside that "for" loop. But the loop can't see the updated value. Then i tried to check if session was actually updated successfully by accessing it from other handlers. And yes it changed, i got the updated value. Only "for" loop can't see this. I tried to change value inside the "for" loop, it also didn't have any effect on session. other handler can't see that change. but only "for" loop can see its changed value. It's like "for" loop using a virtual session of its own. copy the main session before entering the loop, then disconnect it self completely with the session. Notes, I'm using filesystem session, session.modified is set after every change, all library is up to date. manage_session is False... If my words are not clear enough, I'll make a mwe. |
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Replies: 1 comment 4 replies
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There is nothing special about a for loop. The only thing that can prevent the session from being saved is an exception, which would interrupt your handler. |
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from flask import Flask, session, request
from flask_socketio import Namespace
from flask_socketio import SocketIO
from flask_session import Session
app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
app.config['SESSION_TYPE'] = 'filesystem'
sio = SocketIO(app, manage_session=False)
_sess = Session()
_sess.init_app(app)
@app.get('/')
def index():
session['foobar'] = 'A'
return """
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<h1>This is a Heading</h1>
<p>This is a paragraph.</p>
<button type="button" id="stop" >Stop</button>
<button type="button" id="check" >Check</button>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/jquery.min.js" integrity="sha256-/xUj+3OJU5yExlq6GSYGSHk7tPXikynS7ogEvDej/m4=" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/socket.io.min.js" integrity="sha256-crRzk/tlAssAtFB2iE3/ieE1DgXDrc9lW+3rvBM1Wqc=" crossorigin="anonymous"></script>
<script type="text/javascript" charset="utf-8">
var sio = io('/index', {
autoConnect: true,
reconnection: false,
auth: {
token: 'foobar'
},
transports: ['websocket']
});
sio.on("connect", () => {
sio.emit('start');
});
$('#stop').on( "click", function() {
console.log('Stop Clicked?')
sio.emit('stop');
});
$('#check').on( "click", function() {
console.log('Check Clicked?')
sio.emit('check');
});
</script>
</body>
</html>
"""
# noinspection PyMethodMayBeStatic
class IndexSio(Namespace):
def on_connect(self, auth: dict):
print(session[auth['token']])
session[request.sid] = session.pop(auth['token'], None)
print(f'on_connect -> get {session[request.sid]}')
if session[request.sid] is not None:
session[request.sid] = 'on_connect'
print(f'on_connect -> set {session[request.sid]}')
return True
else:
return False
def on_start(self):
for i in range(100):
sio.sleep(3)
print(f'on_start -> get {session[request.sid]}')
session[request.sid] = 'on_start'
print(f'on_start -> set {session[request.sid]}')
def on_stop(self):
print(f'on_stop -> get {session[request.sid]}')
session[request.sid] = 'on_stop'
print(f'on_stop -> set {session[request.sid]}')
def on_check(self):
print(f'on_check -> get {session[request.sid]}')
sio.on_namespace(IndexSio('/index'))
if __name__ == '__main__':
sio.run(app)Print: |
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The session is saved when the handler ends. As I said above, when the loop ends the handler will reach the end, and at that point the session will be saved. |
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Oh. I See. Thanks for explaining. I thought, because session is using filesystem, writing and reading will happen directly to and from the disk. Thread, multi worker... shouldn't matter. Flask-Caching work this way. Anyway, what method would you recommend to stop that loop? Or is it a bad practice to use the loop like that? |
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I don't have the context to answer. A loop in itself is not a problem, but you are using the user session in a strange way. Normally a user session allows an event to store some data that can be retrieved in the future by another event. You are expecting a real-time update of the session to use it as a way of communicating between two running events in parallel. You may want to try using a global variable for that. |
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There is nothing special about a for loop. The only thing that can prevent the session from being saved is an exception, which would interrupt your handler.