There's a chart and some discussion here: http://droettboom.com/blog/2018/04/04/python-in-the-browser/ (and some followup at http://droettboom.com/blog/2018/04/11/profiling-webassembly/ )

TL;DR: pyodide in Firefox was slower than cpython.

Thanks. Note that the author of that post said:

> UPDATE 2018-04-11: My hunch was wrong, and I was able to get to the bottom of the root cause and significantly speed up these benchmarks.

And there's an updated graph here:

http://droettboom.com/blog/2018/04/11/profiling-webassembly/

Certainly for anything using Numpy.

Actually, Numpy-using-code is closer to native speeds than pure Python is.

The thing that seems to cause a greater gap between wasm and native speeds is lots of Python-level function calls, not the tight C loops that make up much of Numpy.

Without a doubt.