[pyxll]

PyXLL (www.pyxll.com) is written using the Excel C API and that’s partly how it achieves its excellent performance. It’s not free software, but it ‘properly’ integrates Python into the Excel process so doesn’t suffer from the performance problems of interacting with Excel from a separate process via COM and VBA.

[ptx]

What about in-process COM? Is that still too slow compared to the C API, or does it have other issues?