Writing Python bindings of existing C libraries – (1) – Introduction

This summer I’m having the pleasure of working in Igalia (a spanish free software company) for a couple of months and they assigned me to an interesting project: developing Python bindings for MAFW library (a Maemo multimedia library that will be used in Fremantle release).

Having the opportunity to work both with C (yes, Python bindings are almost C code) and Python (it’s a good practice to write unittest of all implemented methods) it’s a good way to improve my knowledges in both languages and since I wasn’t able to find much documentation about these kind of things, I’m going to share my own experiences.

What is a Binding?

A binding is a Python module, written in C language, that allows Python developers to call functions from existing C libraries from their python applications. It’s just like a “bridge” from C world to Python one.

Why writing bindings?

There are a couple of reasons to write python bindings instead of writing a library in python language from scratch.

First of all I don’t think is good duplicating code, so if a library already exists and it’s written in C, why writing it again in another language? There’s no reason. A lot of code already exist in C world and all we have to do is to create a bridge with python world.

Another good reason, in particular when a C library doesn’t exist yet, is the fact that python code is slower than C code for some tasks (for example multimedia codecs). In these cases is good to implement the core library in C language and then create a python binding for it.

Coming next

As the title of this post says, this is only an introduction to the subjects I’m going to write about. If you have any particular request about any argument you would like to read, please feel free to leave me a comment. Next posts will talk about these things:

  • A simple example of binding: I’ll write a simple library in C language and I’ll show how to create the relative python binding, providing complete source code and an example for python developers.
  • Building and installing python bindings with distutils: I’ll explain how to use distutils to build and install the binding (using the well know method “python setup.py install”).
  • Defining new types: this post will be about how to write new types in C language and being able to use them from python code.
  • Using codegen to write bindings: I’ll explain how to use codegen utils to automate lot of tasks, to generate the most part of binding code and how to customize the generated code using overrides.

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