Broadcast to all connected clients except sender with python flask socketio

You don't have to save users ids and manage individual emissions, you can specify a broadcast without the sender with emit('my_event', {data:my_data}, broadcast=True, include_self=False). In your case it would be something like this:

@socketio.on('send_message')    def handle_source(json_data):        text = json_data['message'].encode('ascii', 'ignore')        emit('echo', {'echo': 'Server Says: '+text}, broadcast=True, include_self=False)

If you have to send messages for a specific group of clients you can create rooms and then use emit('my_event', {data:my_data}, room=my_room, include_self=False) for sending messages to clients who joined my_room. You can check the reference of flask_socketio.emit for more details.

I can't comment on @Alex's response because I don't have enough reputation, but if you want to emit a broadcast message, this is how it is done in Python:

emit('echo', {'data':'what ever you are trying to send'},  broadcast=True)

https://flask-socketio.readthedocs.io/en/latest/#flask_socketio.SocketIO.emit

You're looking for the skip_sid parameter for socketio.emit().

skip_sid – The session id of a client to ignore when broadcasting or addressing a room. This is typically set to the originator of the message, so that everyone except that client receive the message. To skip multiple sids pass a list.