Introduction to Cython

Cython is a modification of Python that adds C data types. Almost any piece of Python code is also valid Cython code (with a few limitations.) Cython then converts the (modified) Python code into C code which makes equivalent calls to the Python/C API. This C code is then compiled into a shared library which can be imported into Python.

In Cython, function parameters and variables can be declared to have C data types, and code which manipulates Python values and C values can be freely intermixed. Cython takes care of converting from C to Python data types automatically wherever possible. Reference count maintenance and error checking of Python operations is also automatic, and the full power of Python’s exception handling facilities, including the try-except and try-finally statements, is still available.

There are two main benefits of Cython:

Speed

How much performance improves depends very much on the program. Typical Python numerical programs would tend to gain very little as most time is spent in lower-level C anyway. However, for-loop-style programs can improve by many orders of magnitude.

Easy calling into C code

One of Cython’s purposes is to allow easy wrapping of C libraries. When writing code in Cython you can call into C code as easily as into Python code.

The following sections provide a very brief introduction to Cython. See the Cython documentation for a more detailed description of the Cython language and how to use Cython.

Prerequisites

The examples in this lesson can be run directly using the Python interpreter, using IPython interactively, or using Jupyter notebooks. Anaconda users will already have Cython installed. You will also need a functioning C compiler to be able to use Cython. See the Cython installation guide for more details.