Cython

Chapter 3. Cython in Depth

Readability counts.

Special cases aren’t special enough to break the rules.

Although practicality beats purity.

— T. Peters “The Zen of Python”

The preceding chapters covered what Cython is, why we would want to use it, and how we can compile and run Cython code. With that knowledge in hand, it is time to explore the Cython language in depth.

The first two sections of this chapter cover the deeper reasons why Cython works as well as it does to speed up Python code. These sections are useful to help form a mental model of how Cython works, but are not necessary to understand the what of Cython’s syntax, which comprises the remaining sections.

For those interested in why Cython works, it can be attributed to two differences: runtime interpretation versus ahead-of-time compilation, and dynamic versus static typing.

Interpreted Versus Compiled Execution

To better understand how and why Cython improves the performance of Python code, it is useful to compare how the Python runtime runs Python code with how an operating system runs compiled C code.

Before being run, Python code is automatically compiled to Python bytecode. Bytecodes are fundamental instructions to be executed, or interpreted, by the Python virtual machine (VM). Because the VM abstracts away all platform-specific details, Python bytecode can be generated on one platform and run anywhere else. It is up to the VM to translate each high-level bytecode into one or more lower-level operations that can be executed ...