PyScript lets you run Python scripts right in the browser, side by side with JavaScript, with two-way interaction between your code and the web page.

Python might be the most popular programming language in the world, but unlike other frontrunner JavaScript, you can't run Python code in the browser.

Microsoft plans to enable the Python and Ruby languages to be used for client-side development of rich Internet applications that leverage the company’s Silverlight browser plug-in technology ...

It's possible to take a step further with a browser extension, but this is a basic Python project that hosts a web page that you can drag and drop a file on for a visualizer.