I'm certain the host heavy lifting is done by numpy which is a python wrapper around Fortran and C. The visualization heavy lifting is done by pygfx/wgpu-py. wgpu-py has C. I think wgpu-py compiles to WASM to run in the browser. More and more packages are taking this route.
All true, except the bit that wgpu-py compiles to WASM. It's all desktop.
In the plans that we do have for running the browser, Fastplotlib, Pygfx and wgpy-py will still be Python, running on CPython that is compiled to WASM (via Pyodide). But instead of wgpu-py cffi-ing into a C library, it would make JS calls to the WebGPU API.
In fastplotlib at the end of the day everything is wgpu under the hood, and as the other poster correctly pointed out about numpy being fortran and C wrappers.
