reference_existing_object option for pure_virtual c++ classes

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I suck. Sorry for not answering for so long.

Nothing exactly like you want is currently supported. The closest thing is when the parameter is INOUT,

>>> NoddyClass.add_method( 'call_me', ReturnValue.new( 'float' ),
                [Parameter.new('const OtherClass*','n', Parameter.DIRECTION_INOUT)],
                 is_pure_virtual=True )

The resulting output is something like:

float
PyNoddy__PythonHelper::call_me(const OtherClass* n)
{
    ...

    py_OtherClass = PyObject_GC_New(PyOtherClass, &PyOtherClass_Type);
    py_OtherClass->inst_dict = NULL;
    py_OtherClass->flags = PYBINDGEN_WRAPPER_FLAG_NONE;

    // Problem
    py_OtherClass->obj = n;

    ...

    <<< PyObject_CallMethod(...) >>>

   if (py_OtherClass->ob_refcnt == 1) {
       py_OtherClass->obj = NULL;
   } else {
      py_OtherClass->obj = new OtherClass(*n);
   }
  ...
}

So basically it passes a reference to the original object, without copying, and after the call clears the object pointer in the wrapper if the python code hasn't kept a reference to the object, or makes another copy of the object if the python side wants to keep a reference.

If the OtherClass* n parameter is an object that was initially created by python side, then there is another option: wrapper registry. If a wrapper already exists for the object, and wrapper registry is activated (it isn't by default), then a reference to the existing wrapper is used and no object copy is performed (fallback code is written to create the object copy in case a wrapper is not registered yet).

To activate wrapper registry, add this line to your script before generating the code:

    pybindgen.settings.wrapper_registry = pybindgen.settings.StdMapWrapperRegistry