3.7 Embedding Calls

So far, we've seen how to run code typed interactively, and how to launch code saved in files with command lines, icon clicks, IDEs, module imports, and Unix executable scripts. That covers most of the cases we'll see in this book.

But in some specialized domains, Python code may also be run by an enclosing system. In such cases, we say that Python programs are embedded in (i.e., run by) another program. The Python code itself may be entered into a text file, stored in a database, fetched from an HTML page, parsed from an XML document, and so on. But from an operational perspective, another system—not you—may tell Python to run the code you've created.

For example, it's possible to create and run strings of Python code from a C program by calling functions in the Python runtime API (a set of services exported by the libraries created when Python is compiled on your machine):

#include <Python.h>
...
Py_Initialize(  );
PyRun_SimpleString("x = brave + sir + robin");

In this C code snippet, a program coded in the C language embeds the Python interpreter by linking in its libraries, and passes it a Python assignment statement string to run. C programs may also gain access to Python objects, and process or execute them using other Python API tools.

This book isn't about Python/C integration, but you should be aware that, depending on how your organization plans to use Python, you may or may not be the one who actually starts the Python programs you create.^[6] Regardless, you can still likely use the interactive and file-based launching techniques described here, to test code in isolation from those enclosing systems that may eventually use it.

^[6] See Programming Python (O'Reilly) for more details on embedding Python in C/C++. The embedding API can call Python functions directly, load modules, and more. Also note that the Jython system allows Java programs to invoke Python code, using a Java-based API (a Python interpreter class).