本章着眼于从Python访问C代码的问题。许多Python内置库是用C写的，访问C是让Python的对现有库进行交互一个重要的组成部分。这也是一个当你面临从Python 2 到 Python 3扩展代码的问题。虽然Python提供了一个广泛的编程API，实际上有很多方法来处理C的代码。相比试图给出对于每一个可能的工具或技术的详细参考，我么采用的是是集中在一个小片段的C++代码，以及一些有代表性的例子来展示如何与代码交互。这个目标是提供一系列的编程模板，有经验的程序员可以扩展自己的使用。

This code contains a number of different C programming features. First, there are a few

simple functions such as gcd() and is_mandel(). The divide() function is an example

of a C function returning multiple values, one through a pointer argument. The avg()

function performs a data reduction across a C array. The Point and distance() function

involve C structures.

For all of the recipes that follow, assume that the preceding code is found in a file named

sample.c, that definitions are found in a file named sample.h and that it has been compiled

into a library libsample that can be linked to other C code. The exact details of

compilation and linking vary from system to system, but that is not the primary focus.

It is assumed that if you’re working with C code, you’ve already figured that out.