How to Effectively Display Real-time Streamed Data from a Flask View?

How to Display Streamed Data from a Flask View

One common task in web development is to display data that is generated in real time. This data can come from a variety of sources, such as a database, a sensor, or a machine learning model.

In Flask, you can stream data from a view using the yield keyword. This allows you to send data to the client in chunks, rather than waiting for the entire response to be generated. This can be useful for displaying data that is too large to fit in memory, or for displaying data that is constantly changing.

However, one challenge with streaming data is that you can't dynamically update the HTML template as the data is sent. The template is rendered once on the server side, and then sent to the client. This means that you can't use JavaScript to update the template in real time.

There are two main ways to solve this problem:

1. Use JavaScript to read the streamed response and output the data on the client side. This introduces complexity, but it allows updating the page directly and gives complete control over what the output looks like.
2. Use an iframe to display the streamed HTML output. This is a simpler solution, but it has some downsides. The iframe is a separate document, which increases resource usage. Since it's only displaying the streamed data, it might not be easy to style it like the rest of the page. It can only append data, so long output will render below the visible scroll area. It can't modify other parts of the page in response to each event.

Here are some examples of how to implement both solutions:

Using JavaScript to update the page directly

<script>
    var xhr = new XMLHttpRequest();
    xhr.open('GET', '/stream');
    xhr.send();
    xhr.onload = function() {
        if (xhr.status === 200) {
            var data = xhr.responseText;
            // Update the page with the new data
        }
    };
</script>

Using an iframe to display the streamed HTML output

<iframe src="/stream"></iframe>

The best solution for you will depend on your specific requirements. If you need to update the page directly and have complete control over the output, then using JavaScript is the best option. If you need a simpler solution or if you don't need to update the page directly, then using an iframe is a good choice.

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