Question

I have a Python module that I import from my C++ code (I’m embedding Python). This module contains a function create() that I want to get a hold of in my C++ code (i.e. store it in a boost::python::object instance).

Here’s what I tried. A run-time error occurs on the indicated line in my C++ code. The error occurs because it is unable to find the “hero.create” function inside the main namespace.

C++ code

namespace python = boost::python;

// Standard Boost.Python code
// Here I just create objects for the main module and its namespace

python::object main_module(
    python::handle<>(python::borrowed(PyImport_AddModule("__main__")))
);

python::object main_namespace(main_module.attr("__dict__"));


// This is my code
//

python::exec("import hero", main_namespace, main_namespace);
python::object func(main_namespace["hero.create"]); // Run-time error
Entity ent = python::extract<Entity>(func());

// I also tried doing this, but it didn't work either...
// python::object func(main_namespace["hero"].attr("__dict__")["create"]);

// However, if I do this, all works fine...
// python::exec("from hero import create", main_namespace, main_namespace);
// python::object func(main_namespace["create"]); // No error

Python code (hero.py)

from entity import Entity

def create():
    ent = Entity()
    # ...
    return ent

Answer 1

You need to do main_namespace["hero"].attr("create"). Import creates only one name in the namespace, and it’s a module object. Names cannot have dots in them — . is a getattr operator — so hero.create is the same as getattr(hero, 'create').

You could also use boost::python::import directly, instead of execing import statement.