from flask import Flask, render_template
from flask_socketio import SocketIOapp = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app)if __name__ == '__main__':socketio.run(app)

<script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/4.0.1/socket.io.js" integrity="sha512-q/dWJ3kcmjBLU4Qc47E4A9kTB4m3wuTY7vkFJDTZKjTs8jhyGQnaUrxa0Ytd0ssMZhbNua9hE+E7Qv1j+DyZwA==" crossorigin="anonymous"></script>
<script type="text/javascript" charset="utf-8">var socket = io();socket.on('connect', function() {socket.emit('my event', {data: 'I\'m connected!'});});
</script>

@socketio.on('message')
def handle_message(data):print('received message: ' + data)

@socketio.on('json')
def handle_json(json):print('received json: ' + str(json))

@socketio.on('my event')
def handle_my_custom_event(json):print('received json: ' + str(json))

@socketio.on('my_event')
def handle_my_custom_event(arg1, arg2, arg3):print('received args: ' + arg1 + arg2 + arg3)

@socketio.event
def my_custom_event(arg1, arg2, arg3):print('received args: ' + arg1 + arg2 + arg3)

@socketio.on('my event', namespace='/test')
def handle_my_custom_namespace_event(json):print('received json: ' + str(json))

def my_function_handler(data):passsocketio.on_event('my event', my_function_handler, namespace='/test')

@socketio.on('my event')
def handle_my_custom_event(json):print('received json: ' + str(json))return 'one', 2

from flask_socketio import send, emit@socketio.on('message')
def handle_message(message):send(message)@socketio.on('json')
def handle_json(json):send(json, json=True)@socketio.on('my event')
def handle_my_custom_event(json):emit('my response', json)

@socketio.on('message')
def handle_message(message):send(message, namespace='/chat')@socketio.on('my event')
def handle_my_custom_event(json):emit('my response', json, namespace='/chat')

@socketio.on('my event')
def handle_my_custom_event(json):emit('my response', ('foo', 'bar', json), namespace='/chat')

def ack():print('message was received!')@socketio.on('my event')
def handle_my_custom_event(json):emit('my response', json, callback=ack)

@socketio.on('my event')
def handle_my_custom_event(data):emit('my response', data, broadcast=True)

def some_function():socketio.emit('some event', {'data': 42})

from flask_socketio import join_room, leave_room@socketio.on('join')
def on_join(data):username = data['username']room = data['room']join_room(room)send(username + ' has entered the room.', to=room)@socketio.on('leave')
def on_leave(data):username = data['username']room = data['room']leave_room(room)send(username + ' has left the room.', to=room)

@socketio.on('connect')
def test_connect(auth):emit('my response', {'data': 'Connected'})@socketio.on('disconnect')
def test_disconnect():print('Client disconnected')

from flask_socketio import ConnectionRefusedError@socketio.on('connect')
def connect():if not self.authenticate(request.args):raise ConnectionRefusedError('unauthorized!')

from flask_socketio import Namespace, emitclass MyCustomNamespace(Namespace):def on_connect(self):passdef on_disconnect(self):passdef on_my_event(self, data):emit('my_response', data)socketio.on_namespace(MyCustomNamespace('/test'))

@socketio.on_error()        # Handles the default namespace
def error_handler(e):pass@socketio.on_error('/chat') # handles the '/chat' namespace
def error_handler_chat(e):pass@socketio.on_error_default  # handles all namespaces without an explicit error handler
def default_error_handler(e):pass

from flask import request@socketio.on("my error event")
def on_my_event(data):raise RuntimeError()@socketio.on_error_default
def default_error_handler(e):print(request.event["message"]) # "my error event"print(request.event["args"])    # (data,)

socketio = SocketIO(logger=True, engineio_logger=True)