Cython

Chapter 4. Cython in Practice: N-Body Simulation

The programmer, like the poet, works only slightly removed from pure thought-stuff. He builds his castles in the air, from air, creating by exertion of the imagination. Few media of creation are so flexible, so easy to polish and rework, so readily capable of realizing grand conceptual structures.

— F. Brooks

This chapter applies the Cython fundamentals discussed in Chapter 3 to a straightforward but nontrivial example using what we have covered so far. The example starts with a pure-Python N-body simulator to model the solar system, and converts the performance-critical components to use Cython constructs. It comes from the widely known computer language benchmarks game, allowing comparison between the pure-Python, Cython, and C implementations of the same program.

This chapter will give us a better understanding of how Cython is used in practice. The pure-C, pure-Python, and converted Cython versions can be found in the example code repository. Interested readers can follow along with the entire example using this resource.

Overview of the N-Body Python Code

The Python N-body code evolves the positions and velocities of the four Jovian planets in a heliocentric coordinate system. Such a system is chaotic, meaning that the long-term evolution of the system is very sensitive to the initial positions and velocities of all bodies. Small perturbations in the initial conditions lead to arbitrarily diverging results, making prediction difficult. ...