I have successfully wrapped a C++ class, MyObject to Python using Swig.
class MyObject()
{
public:
double i;
};
A MyObject can be created in Python like this:
import MyModule
m = MyModule.MyObject()
The important thing about the above lines is that behind the scenes, the MyObject object is created in the pyd module that is created from C++, and "somewhere", there is a new MyObject() call, returning a pointer to a MyObject object.
Further, the following Python script has a function that returns a Python MyObject, i.e:
import MyModule
def getMyObject():
m = MyModule.MyObject()
#... do something with m, e.g.
m.i = 42
return m
My actual use case is that I initialize the Python interpreter from a C++ application.
I am executing the Python function above,from within my C++ application, i.e.
PyObject *pValue = PyObject_CallObject(pFunc, NULL);
where pFunc is a PyObject* that points to the getMyObject() python function. Code for setting up pFunc omitted for clarity. The returned value should hold a pointer to a MyObject "somewhere".
So question is, how, on the C++ side, do I go from the PyObject* pValue to a MyObject* pointer?
I do have a similar question open, see How to convert a returned Python dictionary to a C++ std::map<string, string>, but that question is more complex, as it involve the conversion from a Python dictionary, to a std class (std::map).
Having a user defined type, like MyObject, would perhaps be the first a user would want to learn to exchange. Curiously, I can't find a simple example showing how todo this.
I'm new to Swig but after doing some research it seem likely that one need to create a typemap?
Also, I'm using Embarcaderos C++ Builder, and can't use any C++11 and/or boost python libraries. Any hints?
Update The following code seem to properly unwrap the C++ object pointer:
PyObject* p = python.callFunction(getPluginMetaDataF);
PyObject* pThis = PyObject_GetAttrString(p, "this");
unsigned long addr = PyLong_AsLong(pThis);
MyObject* ptr = (MyObject*)(addr);
cout << ptr->i; //Prints 42!
The above code seem to properly access the object. However, the life time of the object seem a little shaky, i.e. when is this object destroyed? After Py_Finalize() ??
