CODEWITHSUNDEEP
pythonc++pybind11
pasbi
pasbi

Reputation: 2179

pybind11::object in pybind11::dict

I try to embed a python interpreter into my C++17 application. I must access an object instance of Foo, which lives in the C++-world, from python.

So I came up with following code:

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

namespace py = pybind11;
using namespace py::literals;

class Foo
{
public:
  Foo() : v(42) {}
  int get() const { return v; }
  void set(int x) { v = x; }
private:
  int v;
};

PYBIND11_EMBEDDED_MODULE(my_module, m) {
    py::class_<Foo>(m, "Foo")
      .def(py::init<>())
      .def("get", &Foo::get)
      .def("set", &Foo::set);
}

int main()
{
  py::scoped_interpreter guard{};
  using namespace py::literals;

  py::object py_foo = py::cast(Foo());
  auto locals = py::dict(
    "foo"_a = py_foo            // (line of evil)
  );

  // CRASH!
  try {
    py::exec("print(foo.get())", py::globals(), locals);
    return EXIT_SUCCESS;
  } catch (const std::exception& e) {
    std::cerr << e.what() << std::endl;
    return EXIT_FAILURE;
  }
}

which crashes at runtime: Unable to convert call argument 'foo' of type 'object' to Python object

The docs only show how to insert int and string into a py::dict.

I guess pybind11 knows about Foo, since when I remove the line (line of evil) and replace the code with from my_module import Foo; print(Foo().get()), it does what I expect (but obviously not what I intend).

So, what am I doing wrong?

Upvotes: 2

Views: 3119

Answers (1)

llllllllll
llllllllll

Reputation: 16444

In embedded Python interpreter, you need to import the module first, otherwise Python doesn't know that module exists.

Add py::module::import("my_module"); to your main():

int main()
{
  py::scoped_interpreter guard{};

  py::module::import("my_module");  // <-- Here, import the module
  using namespace py::literals;

  py::object py_foo = py::cast(Foo());
  auto locals = py::dict(

// ....

Upvotes: 5

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