[C++-sig] Nested Boost::Python dictionaries

[Jim Bosch]

On 05/12/2012 12:22 PM, DarkAnt wrote:
> I'm trying to create a boost::python::dict that stores another
> boost::python::dict.
>
> int main()
> {
> 	Py_Initialize();
> 	boost::python::dict parent;
> 	try{
> 		parent["child_dict"] =
> boost::make_shared<boost::python::dict>(boost::python::dict());
> 	}
> 	catch(...){
> 		PyErr_Print();
> 	}
> 	return 0;
> }
>
> TypeError: No to_python (by-value) converter found for C++ type: class
> boost::shared_ptr<class boost::python::dict>
>
> I was under the impression that boost::shared_ptr had special
> treatment in boost::python(that is the library already knew what to do
> with it). I'm not quite sure if I'm supposed to write this to_python
> converter or if I'm supposed to achieve this in a different manner. If
> I do write the to_python converter what's the method of keeping track
> of both reference counts?

There's no need to use shared_ptr on Python objects; those will be 
tracked using Python's own reference counting system.

Just doing

parent["child_dict"] = boost::python::dict();

will do what you want.

Note that boost::python::dict (as well as boost::python::object, etc.) 
is actually a smart pointer itself, holding a PyObject* and 
incrementing/decrementing the reference count in the C++ copy 
constructor, assignment operator, and destructor.

HTH!

Jim