Pure Python & Flask server-side event source

index.html

<script>
var stream = new EventSource('/api/stream');
stream.onmessage = function(e) {
    console.info(e.data);
};
</script>

server.py

from queue import Queue
from flask import Flask, render_template, request

app = Flask(__name__)
app.debug = True

queue = Queue()

def event_stream():
    while True:
    	# Question: how to break out of this loop when the app is killed?
        message = queue.get(True)
        print("Sending {}".format(message))
        yield "data: {}\n\n".format(message)


@app.route('/')
def hello():
    return render_template('index.html')


@app.route('/api/stream')
def stream():
    return flask.Response(event_stream(), mimetype="text/event-stream")


@app.route('/api/post', methods=['GET'])
def api_parse_sentence():
    queue.put(request.args.get('sentence'))
    return "OK"


if __name__ == '__main__':
    app.run(threaded=True)

@eliwjones That's a very fair point. Hadn't encountered that yet, but makes total sense. Thanks for the revision.

You're also right that this won't work for more than a very simple test setup (in case of your example, QUEUES would just keep on growing and all queues that won't be listened to anymore will keep getting saturated). So let that be a warning to anyone wanting to use this snippet :)