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CHAPTER 17 ■ EXTENDING PYTHON 371
SWIG. SWIG is a tool for automatically generating wrapper code for your C libraries. The
wrapper code takes care of the Python C API so you don’t have to. It is one of the easiest
and most popular ways of extending Python.
Using the Python/C API. You can write C code yourself that can be imported directly into
Python as shared libraries. To do this, you have to adhere to the Python/C API. Things you
have to take care of for each function include reference counting, extracting arguments,
and building return values. There is also a certain amount of code needed to make a C
library work as a module, including listing the functions in the module and creating a
module initialization function.
New Functions in This Chapter
Function
Py_INCREF(obj)
Py_DECREF(obj)
PyArg_ParseTuple(args, fmt, ...)
PyArg_ParseTupleAndKeywords(args, kws, fmt, kwlist)
PyBuildValue(fmt, value)
Description
Increment reference count of obj
Decrement reference count of obj
Extract positional arguments
Extract positional and keyword
arguments
Build a PyObject from a C value
What Now?
Now you ought to either have some really cool programs or at least some really cool program
ideas. Once you’ve got something you want to share with the world (and you do want to share
your code with the world, don’t you?), the next chapter can be your next step.