How to cast a python function to std::function with pybind11

Question

I have a c++ type Foo which contains a std::function<void()> funcs , which has been successfully bound to python. My aim is to define functions in python and add them to this type, then return an instance. In c++ I use pybind to get an instance of this type which works. However when I attempt to call one of the functions my program seg-faults.

class Foo
{
    void addFunc(std::function<void()> _func)
    {
      funcs.push_back(_func);
    }

    void call(int _index)
    {
      funcs[_index]();
    }

private:
    std::vector<std::function<void()>> funcs;
}

namespace py = pybind11;

PYBIND11_MODULE(foo, m) 
{
    py::class_<Foo>(m, "foo")
        .def(py::init<int, int>())
        .def("addFunc", &Foo::addFunc)
        .def("call", &Foo::call);
}

And later in c++

py::scoped_interpreter python;
auto module = py::module::import("foo_module");
auto func = module.attr("create_foo");
auto result = func();
//This works!
result.attr("call")(0);
Foo* blah = result.cast<Foo*>();
//This seg-faults!
blah->call(0);

My python module has this:

def newFunc():
    print "working!"

def create_foo():

  temp = foo.Foo(0, 100)
  temp.addFunc(newFunc)
  return temp

I'm not sure why the functions aren't being cast back to c++ correctly?

Answer 1

I had to move the py::scoped_interpreter python; to a higher scope as it wasn't in scope when the function was called