How to Efficiently Stream Real-time Data from a Flask View into an HTML Template?

Streaming Data into an HTML Template

When working with real-time data streamed from a Flask view, it's natural to want to display it in a dynamic HTML template. However, traditional template rendering techniques fall short as the template is rendered once on the server-side and sent in its entirety to the client.

Using JavaScript for Dynamic Display

One solution to this issue is to utilize JavaScript for client-side updates. By making an XMLHttpRequest request to the streaming endpoint, you can read the data incrementally and output it directly to the page. This approach allows for real-time updates and complete control over the display format.

Here's an example using JavaScript:

Python (server-side):

from flask import Flask, Response

app = Flask(__name__)

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

@app.route('/stream')
def stream():
    def generate():
        for i in range(10):
            yield str(i) + '\n'
    return Response(generate(), mimetype='text/plain')

HTML (client-side):

<p>This is the latest output: <span>

Using an Iframe for HTML Streaming

An alternative approach involves using an iframe to display streamed HTML output. While this technique allows for dynamic rendering, it comes with drawbacks:

• Adds complexity due to separate document context
• Limited styling options
• Potential rendering issues with long output

In this method, the index.html file would contain:

<p>This is all the output:</p>
<iframe src="{{ url_for('stream') }}"></iframe>

And the stream view in Python would be:

from flask import stream_with_context

@app.route('/stream')
def stream():
    @stream_with_context
    def generate():
        yield '<link rel=stylesheet href="{{ url_for('static', filename='stream.css') }}">'
        for i in range(10):
            yield render_template_string('<p>{{ i }}: {{ s }}</p>\n', i=i, s=sqrt(i))

In this example, CSS is loaded first in the iframe using render_template_string, and the HTML content is streamed incrementally.

The above is the detailed content of How to Efficiently Stream Real-time Data from a Flask View into an HTML Template?. For more information, please follow other related articles on the PHP Chinese website!