There was a project announced this week that lets you write python scripts in HTML and have them execute in the browser (pyscript). Here's an example.
<body> Hello world! <br> This is the current date and time, as computed by Python: <py-script> from datetime import datetime now = datetime.now() now.strftime("%m/%d/%Y, %H:%M:%S") </py-script>
But what language will become the new lingua franca of the web?
It's no longer necessary to have a just-in-time compiled scripting language. Instead, you can ship binary blobs compiled down to WebAssembly from various languages.
Python in the browser has passed the prototype phase but will need a "compiled" form (If it can be compiled, it will be). Either some format like the PAR file or a webpack-like bundler system.