EMBEDDING THE CPYTHON RUNTIME IN A LARGER APPLICATION 3.1 Embedding Python in Another Application 3.1.1 Very High Level Embedding CHAPTER THREE Sometimes, rather than creating an extension that runs inside the Python interpreter as the main application, it is desirable to instead embed the CPython runtime inside a larger application. This section covers some of the details involved in doing that successfully. The previous chapters discussed how to extend Python, that is, how to extend the functionality of Python by attaching a library of C functions to it. It is also possible to do it the other way around: enrich your C/C++ application by embedding Python in it. Embedding provides your application with the ability to implement some of the functionality of your application in Python rather than C or C++. This can be used for many purposes; one example would be to allow users to tailor the application to their needs by writing some scripts in Python. You can also use it yourself if some of the functionality can be written in Python more easily. Embedding Python is similar to extending it, but not quite. The difference is that when you extend Python, the main program of the application is still the Python interpreter, while if you embed Python, the main program may have nothing to do with Python — instead, some parts of the application occasionally call the Python interpreter to run some Python code. So if you are embedding Python, you are providing your own main program. One of the things this main program has to do is initialize the Python interpreter. At the very least, you have to call the function$_{Py_Initialize()}$ . There are optional calls to pass command line arguments to Python. Then later you can call the interpreter from any part of the application. There are several different ways to call the interpreter: you can pass a string containing Python statements to PyRun_SimpleString() , or you can pass a stdio file pointer and a file name (for identification in error messages only) to$_{PyRun_SimpleFile()}$ . You can also call the lower-level operations described in the previous chapters to construct and use Python objects. c-api-index The details of Python’s C interface are given in this manual. A great deal of necessary information can be found here. See also: The simplest form of embedding Python is the use of the very high level interface. This interface is intended to execute a Python script without needing to interact with the application directly. This can for example be used to perform some operation on a file. #define PY_SSIZE_T_CLEAN #include<Python.h> int (continues on next page) 59