Book Image

Learning Cython Programming (Second Edition) - Second Edition

By : Philip Herron
Book Image

Learning Cython Programming (Second Edition) - Second Edition

By: Philip Herron

Overview of this book

Cython is a hybrid programming language used to write C extensions for Python language. Combining the practicality of Python and speed and ease of the C language it’s an exciting language worth learning if you want to build fast applications with ease. This new edition of Learning Cython Programming shows you how to get started, taking you through the fundamentals so you can begin to experience its unique powers. You’ll find out how to get set up, before exploring the relationship between Python and Cython. You’ll also look at debugging Cython, before moving on to C++ constructs, Caveat on C++ usage, Python threading and GIL in Cython. Finally, you’ll learn object initialization and compile time, and gain a deeper insight into Python 3, which will help you not only become a confident Cython developer, but a much more fluent Python developer too.
Table of Contents (14 chapters)
Learning Cython Programming Second Edition
About the Author
About the Reviewer

Keyword cpdef

So far, we have seen two different function declarations in Cython, def and cdef, to define functions. There is one more declaration—cpdef. The def is a Python-only function, so it is only callable from Python or Cython code blocks; calling from C does not work. The cdef is the opposite; this means that it's callable from C and not from Python. For example, if we create a function such as:

cpdef public test (int x):
  return 1

It will generate the following function prototype:

__PYX_EXTERN_C DL_IMPORT(PyObject) *test(int, int __pyx_skip_dispatch);

The public keyword will make sure we generate the needed header so that we can call it from C. Calling from pure Python, we can work with this as if it was just any other Python function. The drawback of using cpdef is that the native return type is PyObject *, which requires you to know exactly what the return type is and consult the Python API documentation to access the data. I prefer keeping bindings between the languages simpler...