Wsrtjtyk

I built a WSGI page that contains both tabulated data and a scatterplot of the same data from a database. (I'm using flask and matplotlib but that doesn't matter). This generates two separate requests: One for the HTML page and one for the dynamically generated image called from the tag. Since the database is rather slow and since both requests need exactly the same data I'd like to make this work with just one SQL query. Two approaches come to mind:

1. After querying the DB in the HTML view function, generate the scatterplot and save that in a PNG file somewhere. Then pass the tabulated data on to the template and serve up the cached PNG once the browser requests the image.




2. Somehow embed the image data in the HTML itself and have the browser render it using Javascript.

Approach 1. is simple and straightforward, but I also need a way to get rid of the cached images when they are not needed any more. This is prone to get messy. Since the app is purely http-request driven I would have to scan my cache dir on each request and decide which file is old enough to be deleted. Alternatively I could have an "onload" javascript function call my app a third time to trigger deletion of the image. Maybe clever, but robust?

2. I have no idea how to do this, let alone in a browser-compatible way.

Any suggestions?

I've been on Usenet for 25 years and still posting a question is the best method to find the answer yourself after a few minutes:

<img src="data:image/png;base64, {{imgdata}}">

and in the view function:

return flask.render_template('chart_page.html', imgdata=base64.b64encode(pixbuf))

End of story. No javascript.