Classic Python runs on a portable C-coded virtual machine. Python's built-in objects, such as numbers, sequences, dictionaries, and files, are coded in C, as are several modules in Python's standard library. Modern platforms support dynamic-load libraries, with file extensions such as .dll on Windows and .so on Linux, and building Python produces such binary files. You can code your own extension modules for Python in C, using the Python C API covered in this chapter, to produce and deploy dynamic libraries that Python scripts and interactive sessions can later use with the import statement, covered in Chapter 7.
Extending Python means building modules that Python code can import to access the features the modules supply. Embedding Python means executing Python code from your application. For such execution to be useful, Python code must in turn be able to access some of your application's functionality. In practice, therefore, embedding implies some extending, as well as a few embedding-specific operations.
Embedding and extending are covered extensively in Python's online documentation; you can find an in-depth tutorial at http://www.python.org/doc/ext/ext.html and a reference manual at http://www.python.org/doc/api/api.html. Many details are best studied in Python's extensively documented sources. Download Python's source distribution and study the sources of Python's core, C-coded extension modules and the example extensions supplied for study purposes.
This chapter covers the basics of extending and embedding Python with C. It also mentions, but does not cover, other possibilities for extending Python.