Anvil (https://anvil.works/) is probably the closest thing to what you are looking for, at least in the python world.

See https://streamlit.io/

Check out https://www.pyweb.io/

To make it run entirely in the user's browser, you need to have the Python interpreter and any additional libraries running on the user's machine. This is the case with Javascript but not Python.

look at https://pywebio.readthedocs.io/en/latest/

This actually has a web backend.