PyScript, which is, of course, Python in the browser. The tool is in the early experimental phase, so the project doesn’t suggest using it in a production environment yet.

Playwright, a Python library, allows developers to essentially control the browser with a few lines of Python code to automate cross-browser testing for single-page web apps and Progressive Web Apps.

A new project from Anaconda delivers the Python runtime in a web page, via a single JS include, and with access to many popular Python packages.

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.