Exposing C++ to Python

How to expose c++ functionality to Python
It becomes necessary at times to expand the FreeCAD API further by exposing functions that are available in the source code in c++ to the python. In so doing, providing an ability to trigger deep internal functionality with Python in real-time instead of needing to compile.

Below is an explanation of how one can achieve this.

The basic structure of a program to expose functionality to Python is something like this:


 * get the Py object parameters and convert them to c++ variables using PyArg_ParseTuple,
 * use various c++ routines from OpenCascade and/or FreeCAD to produce the desired result,
 * convert the c++ result into Py object using routines like PyLong_AsLong, Py::asObject, etc,
 * return the Py object.

Source: https://forum.freecadweb.org/viewtopic.php?p=314796#p314617

There are two source files required to implement a new Python binding. Assuming we wanted to expose some methods from .../Mod/Part/TopoShape.cpp, we would need to make: These 2 files need to be added to .../Mod/yourModule/App/CMakeLists.txt. See .../Mod/Part/App/CMakeLists.txt for an example.
 * TopoShapePy.xml - definitions of the functions for be exposed in XML format. This file is used to generate header files for our next file...
 * TopoShapePyImp.cpp - the actual C++ code that bridges from Python to C++.

You can extend the Python version of your module by adding to ../Mod/myModule/App/AppmyModulePy.cpp (see ../Mod/Part/AppPartPy.cpp). The additions are accessed in Python by "import myModule".

Note: xxxxxPyImp routines return a PyObject* pointer (see TopoShapePyImp.cpp) and AppmyModulePy.cpp routines return a Py::Object (see ../Mod/Part/AppPartPy.cpp).