This also isn't necessarily true. Take the example of TensorFlow. You build a representation of the computation you want to run, and then you can run nearly the

This also isn't necessarily true. Take the example of TensorFlow. You build a representation of the computation you want to run, and then you can run nearly the whole thing end-to-end in native C++ using Eigen data structures, with occasional shuttling of data back into PyObjects (rare) or numpy (common) for metrics tracking. Cython is a much more powerful tool than I think the author of this article realizes.