A possible approach is to use Cython to convert Python code to C code and then compile that code to WebAssembly. I would not be surprised if there is a tool for that already
from my experience digging through Cython output: unless you type-annotate EVERYTHING C-style, Cython just uses the CPython C-API (PyObject_New, PY_INCREF, etc). so you'd have to ship all of CPython anyway... as mentioned elsewhere in the thread, that's too big for most websites