Periodic long polling with while loop [duplicate]

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    Vote count: 4

    I have a view that generates data and streams it in real time. I can't figure out how to send this data to a variable that I can use in my HTML template. My current solution just outputs the data to a blank page as it arrives, which works, but I want to include it in a larger page with formatting. How do I update, format, and display the data as it is streamed to the page?

    import flask
    import time, math
    
    app = flask.Flask(__name__)
    
    @app.route('/')
    def index():
        def inner():
            # simulate a long process to watch
            for i in range(500):
                j = math.sqrt(i)
                time.sleep(1)
                # this value should be inserted into an HTML template
                yield str(i) + '
    n' return flask.Response(inner(), mimetype='text/html') app.run(debug=True)
    edited Aug 11 '15 at 20:18
    davidism
    asked Aug 11 '15 at 17:30
    JeffThompson

    1 Answer

    Vote count: 6 accepted

    You can stream data in a response, but you can't dynamically update a template the way you describe. The template is rendered once on the server side, then sent to the client. You'll need to use JavaScript to read the streamed response and output the data on the client side.

    Use XMLHttpRequest to make a request to the endpoint that will stream the data. Then periodically read from the stream until it is done.

    This example assumes a very simple message format: a single line of data, followed by a newline. You can of course get as complicated in parsing as you like, as long as there's a way to identify each message. For example, you could return a JSON object and decode it on the client.

    from time import sleep
    from flask import Flask, render_template
    from math import sqrt
    
    app = Flask(__name__)
    
    @app.route('/')
    def index():
        # render the template (below) that will use JavaScript to read the stream
        return render_template('index.html')
    
    @app.route('/stream_sqrt')
    def stream():
        def generate():
            for i in range(500):
                yield '{}n'.format(sqrt(i))
                sleep(1)
    
        return app.response_class(generate(), mimetype='text/plain')
    
    app.run()
    

    This is the latest output:

    This is all the output:

      answered Aug 11 '15 at 20:11
      davidism
      نویسنده : استخدام کار بازدید : 0 تاريخ : جمعه 21 مهر 1396 ساعت: 8:22
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