pybind11 realize a cpp middleware concept (basics) - c++

Question

CPP Middleware in a python enviroment
I Want to realize this structure.
App (python) <-> Middleware (cpp) <-> Driver (python)
A App (python) will access some middleware classes in CPP. And then use a driver (python).
App.py
import pybind_11_example as middleware_cpp
n = 40
print('C++:')
print('Answer:', middleware_cpp.testFunctionA_cpp(n))
Middleware.h
#include <pybind11/pybind11.h>
class middleware
{
public:
unsigned int testFunctionA(const unsigned int n);
namespace py = pybind11;
PYBIND11_MODULE(pybind_11_example, mod) {
mod.def("testFunctionA_cpp", &testFunctionA, "Middleware class.");
}
Middleware.cpp
#include "Middleware.h"
#include "stdio.h"
#include <pybind11/pybind11.h>
#include <pybind11/embed.h> // python interpreter
#include <pybind11/stl.h> // type conversion
unsigned int middleware::testFunctionA(const unsigned int n)
{
printf("Now Sent back to python driver interface\n");
//py::scoped_interpreter guard{}; // start interpreter, dies when out of scope
py::module driver= py::module::import("Driver");
py::object result = driver.attr("setValue")("setting value from cpp to python driver");
return 42;
}
Driver.py
class Driver:
def __init__(self):
print ("Init Driver Class")
self.name = "This is the Driver Class"
def printMyClass(self):
print(self.name)
def setValue(self, value):
print(value)
I have read the docs but did this example not working. So i want to place it here as a example template if other want also try this approach.
Question 1:
How do I call the python Driver class function "setValue" from cpp?
The current implementation from Middleware.cpp calling the function setValue leads to this error:
AttributeError: module 'Driver' has no attribute 'setValue'
Question 2:
Calling the interpreter twice should not be needed, because it is assumed, the the middleware is accessed from the running app process, which is already in python.
py::scoped_interpreter guard{}; // start interpreter, dies when out of scope
Best regards Holger