How to return a pointer to a C++ object to python using boost if the class of that object is declared in another boost module?

Question

Okay, maybe I'm not finding an answer because I'm not sure how to word it, but I have a class called Info and another class called Packet, both are compiled into Python extensions using boost, and I would like to return a pointer to an Info object from the Packet module.

info.cpp

#include "info.h"
Info::Info(int i_, int j_){
    this->i = i_;
    this->j = j_;
} 

Info::~Info(){
}

BOOST_PYTHON_MODULE(Info)
{
    class_<Info>("Info", init<int, int>())
    .def_readwrite("i", &Info::i)
    .def_readwrite("j", &Info::j);
}

Packet.cpp:

Packet::Packet(int i_, int j_, PyObject* addr_, bool a_, bool b_){
    this->i = i_;
    this->j - j_;
    this->addr = addr_;
    this->a = a_;
    this->b = b_;
}
// some other functions

Info* Packet::test(){
    return new Info(1,2);
}
BOOST_PYTHON_MODULE(Packet)
{
    class_<Packet>("Packet", init<int, int, PyObject*, bool, bool>())
        /*some other functions*/
        .def("test", &Packet::test, return_value_policy<reference_existing_object>());
}

testPacket.py:

from Packet import *
# this works correctly
p = Packet(1,2, None, False, False)
# this crashes
t = p.test()

error message:

Traceback (most recent call last):
  File "/usr/lib64/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib64/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/tmp/lirui/testPacket.py", line 5, in <module>
    print(p.test())
TypeError: No Python class registered for C++ class Info

Is there any way I can return a pointer to an Info object?

Thanks

Don't you need to import Info too? It says right there it isn't registered... I don't know this technology well, though. — Asteroids With Wings
– Asteroids With Wings, Commented Jul 7, 2020 at 21:05
hey that worked, I thought all I needed was to import it in the .cpp and link them toghether in the makefile... thanks! — qwerty_99
– qwerty_99, Commented Jul 7, 2020 at 21:08

Asteroids With Wings · Accepted Answer · 2020-07-07 21:09:53Z

2

You only imported Packet.

You also need to import Info.

Otherwise, as the error says, Python doesn't recognise it when p.test() attempts to use it (or, more specifically, to return a pointer to it, to assign to t).

answered Jul 7, 2020 at 21:09

Asteroids With Wings

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