There is a minimal amount of JavaScript just to download and run pyodide and then it is only Python: see example at

https://imgui-bundle.pages.dev/playground/?demo=p_35_minimal...

Yes, the initial download of pyodide is about 5 MB. After that it is another 5MB for the bundle wheel.

But there is some hope: Based on test I just did, I see I did not setup headers so that the wheel and pyodide are cached in a browser (or in its fs): this could reduce reload times by a sizable factor.

Once loaded you can run at 60 FPS (or even 120 FPS depending on the browser's vsync).

As you can see in the playground: you can then switch from app to app instantly once pyodide is loaded and running. It almost feels like going from a page to another. You can see that when using the combobox to select example at the top right in the playground.

As an example, I once built an online stock/ticker app with it: smooth real-time updates in a nice plot. It would have been more complex with DOM based widgets (and probably less fun).

What I do not like is the strange mix of technologies you have to cope with in order to work with Python on the web: your project is often a mix of python / html / css / react / js / node.

Many very nice frameworks try to abstract this and present you only the python side; but they rely on this stack internally. Once you want to reach complex use cases (such as a refresh at reasonable rate), you will have to "open the engine" and enter into this mix.