Is there a performance hit compared to "native" Python?
TL;DR: pyodide in Firefox was slower than cpython.
> 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/
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.