How to bind two nested structures using pybind11

Question

typedef struct _Names
{
    int a;
    int b;
    int c;
} Names;

typedef struct _values
{
    Names names;
}values;

binding code I have is

py::class_<Names>(m, "Names")
    .def(py::init<>())
    .def_readwrite("a", &Names::a)
    .def_readwrite("b", &Names::b)     
    .def_readwrite("c", &Names::c);

py::class_<values>(m, "values")
    .def(py::init<>()) 
    .def_readwrite("names", &values::names);
    

but I am unable to access names.a or names.b or names.c.

How can I bind names with Names structure?

Answer 1

welcome to SO!

Hum, it should work. My guess is that your python code doesn't instantiate the class values correctly.

I have

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

namespace py=pybind11;

typedef struct _Names
{
    int a;
    int b;
    int c;
} Names;

typedef struct _values
{
    Names names;
} values;


// Wrapping code
PYBIND11_MODULE(wrapper, m) {
    py::class_<Names>(m, "Names")
        .def(py::init<>())
        .def_readwrite("a", &Names::a)
        .def_readwrite("b", &Names::b)
        .def_readwrite("c", &Names::c);

    py::class_<values>(m, "values")
        .def(py::init<>())
        .def_readwrite("names", &values::names);
}

And if I compile it (see example 1 in this github repo if you need directions) to a file called wrapper, I can use it from python as

import wrapper

b = wrapper.values()  # <-- don't forget the parenthesis !
b.names.a = 30
print(b.names.a)  # prints 30

I'm guessing you didn't put parenthesis after wrapper.values which causes (in my case) b to contain the class definition instead of an instance of it.

Hope it helps :)