Cython is used all over the place in some parts of the real world, but you may not hear about those parts because they are not that connected to web app develop

Cython is used all over the place in some parts of the real world, but you may not hear about those parts because they are not that connected to web app development. The entire scientific Python ecosystem has basically moved on to Cython. Its use is quite prevalent, and it's basically displacing SWIG as the preferred wrapping tool of choice.