[dagw]

That is true, but there are relatively few real world applications that consist of only those operations. In the example I mentioned below, there where actually some parts of my python rewrite that ended up faster than the original C++ code, but once everything was strung together into a complete application those parts where swamped by the slow parts.

[ghostwriter]

Most of the time these are arithmetic tight loops that require optimisations, and it's easy to extract those into separate compiled cython modules without losing overal cohesion within the same Python ecosystem.