Comment by edsac_xyzw

This duct type is the Python native extension api (not python ctypes) which allows creating native code modules (aka libraries) in C or C++ and creating wrappers to existing C or C++ libraries. This escape hatch that enables offloading cpu-intensive computations to high performance libraries written in C, C++ or Fortran. Another benefit of python modules written in C or C++ is that they are not affected by the GIL (Global Interpreter Lock) problem, thus they can take advantage of multi-core and SIMD instructions and achieve higher performance.