My problem is as follow: I have a C++ code that I can't modify as I want (not written by me and under some intellectual property constraints). I have to link it with a Python code through a Python main. I use boost::python for the reflection. At some point in the code, a C++ function use a Python overloaded function of a C++ function to modify a parameter. This function works great when used inside Python. But when called by a C++ function, the modification of the parameter will not be taken into account while back in C++. To model the problem, I wrote a simplified version aimed at isolating my problem.
Here are the C++ classes:
#include <iostream>
using namespace std;
#include <boost/ref.hpp>
//Class aimed at modeling a C++ user's type that should be used in Python
class C
{
public:
double myC;
C(){}
~C(){}
void setValue(double val) {
myC = val;
}
double getValue() {
return myC;
}
};
/*
This class will be derived in Python
We want to be sure that:
- void (g) and non void (f) functions are properly reflected and extended in Python
- a function (h) with a local type (C) will properly use the python overloaded function of a C++ function (g)
*/
class A
{
public:
A(){int A_x=0;}
virtual ~A(){}
virtual int f(int Ivar){
Ivar = 0;
return Ivar;
}
virtual void g(C * myC){
C calledC;
cout << "I should not be here" << endl; //When B::setparam call g, it should be the Python g, not the virtual function from base class
calledC.setValue(0.);
//return *myC;
}
C h(){ //This function wont be overloaded in Python
C myC;
//myC.setValue(0.);
this->g(&myC); //We want myC to be modified, and the python overloaded version of g to be used
cout << "Value back in C++: " << myC.getValue() << endl; //We want to verify if myC has been modified back in C++
return myC;
}
};
/*
This class will be called from a main in Python.
It's function setparam is aimed at ensuring that Python extension of a C++ class is supported properly
*/
class B
{
public:
B(A & a){
setparam(a);
}
B(){
int u;
u = 0;
}
virtual ~B(){}
void setparam(A & a){
a.h(); //Here the code should call the h overloaded function of the derived class of A in Python
}
};
The boost::python wrapper:
#include <boost/python.hpp>
#include <Python.h>
#include <object.h>
#include "ClassA.h"
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/implicit.hpp>
#include <iostream>
using namespace std;
using namespace boost::python;
/*
A wrapper is used to allow overload of virtual A function
*/
struct WrapperClassA : A, boost::python::wrapper<A>{
int f(int Ivar){
if(override f = this->get_override("f")){
return f(Ivar);
}
else {
return A::f(Ivar);
}
}
int default_f(int Ivar){
return this->A::f(Ivar);
}
void g(C * myC){
if(override g = this->get_override("g")){
g(myC);
}
else {
A::g(myC);
}
}
void default_g(C * myC){
this->A::g(myC);
}
};
/*
Refection of necessary classes and functions for Python
*/
BOOST_PYTHON_MODULE(myWrapper){
class_<WrapperClassA, boost::noncopyable>("A", init<>())
.def("f", &A::f, &WrapperClassA::default_f)
.def("g", &A::g, &WrapperClassA::default_g)
;
class_<B, boost::noncopyable>("B", init<>())
.def("setparam", &B::setparam)
;
class_<C>("C", init<>())
.def("setValue", &C::setValue)
.def("getValue", &C::getValue)
.def_readwrite("myC", &C::myC)
;
}
The python code:
from math import *
# C++ library
from myWrapper import *
"""
Extension of C++ class A
APy should be used when A type argument is called
g should be able to use a C++ C type object and to modify it
The constructor call g in order to verify that myC is treated as mutable within Python
"""
class APy(A):
def __init__(self):
A.__init__(self)
n = 0
x = 0.
myC = C()
self.g(myC)
print("value after a 1st call within Python: " + repr(myC.getValue()))
def f(self, n):
n = 5
return n
def g(self, myC):
x = 7.0
myC.setValue(x)
print("value in Python: " + repr(myC.getValue()))
"""
Main
myB.setparam should be able to pass a APy argument
"""
myA = APy()
myB = B()
myB.setparam(myA)
When I run the code, print("value in Python: " + repr(myC.getValue())) print 7, but cout << myC.getValue() << endl print 0 while I would like the variable to be at 7. Thank you for any help.
