How to convert a python class into a C++ class in pybind11 where there is a list of node pointers in the member variables.

[LJHG]

I'm trying to convert a python object to a cpp object for processing in cpp code. Here's what I met.

I create a class in cpp where one of the member is sons, containing 3 pointers of the object itself, the other is location, meaning the (x,y,z) location of the Node. Also, I create a corresponding class in python.

My target is to convert a python object into a cpp object, so I write a function called Node_p2cpp.

The problem I met is that after conversion, the cpp object became very weird, the location of the sons is randomly changing all the time, and the number of the sons is not right, sometimes may throw a RuntimeError: Could not allocate list object! bug.

What is going on? Any help would be appreciated! And here's the minimum executable code.

example.cpp

#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <iostream>


namespace py = pybind11;
using namespace std;

struct Node{
  vector<Node*> sons;
  vector<float> location;
  Node(vector<Node*> _sons,vector<float> _location){
    sons = _sons;
    location = _location;
  }
};

PYBIND11_MODULE(example, m) {
    m.doc() = "pybind11 example plugin"; // optional module docstring

    py::class_<Node>(m,"Node")
      .def(py::init<vector<Node*>,vector<float>>())
      .def_readwrite("sons",&Node::sons)
      .def_readwrite("location",&Node::location);
}

example.py

import example
class Node:
    def __init__(self, sons, location):
        self.sons = sons #suppose everynode has 3 sons
        self.location = location # (x,y,z) coordinate

def Node_p2cpp(Node):
    sons = []
    for i in range(3):
        if(Node.sons[i] is not None):
            sons.append(Node_p2cpp(Node.sons[i]))
        else:
            sons.append(None)
    new_Node = example.Node(sons,Node.location)
    return new_Node


Node1 = Node([None,None,None],[0.1,0.1,0.1])
Node2 = Node([Node1,None,None],[0.2,0.2,0.2])
root = Node([Node2,None,None],[0.3,0.3,0.3])

print("location and number of sons of the first son before conversion...")
print(root.sons[0].location)

print("location and number of sons of the first son after conversion...")
cpp_root = Node_p2cpp(root)
print(cpp_root.sons[0].location)