On 10/14/11 10:29, Holger Joukl wrote:
Hi,
currently i am facing a problem regarding inheritance with boost::python
Here is a simple code snippet:
class Base
{
public:
virtual void print() { std::cout<< "hello"<< std::endl; }
};
[...]
And in python i want to have the following reslut:
>>import my_module
>> derived = my_module.Derived()
>> derived.printIt()
Actually this should print "hello" but instead throws an error saying:
derived.printIt()
Boost.Python.ArgumentError: Python argument types in
Base.printIt(Derived)
did not match C++ signature:
printIt(_Base {lvalue})
Maybe I'm oversimplifying but if all you need is exposing some derived
class then
I don't see why you'd need all the BaseWrapper, self-pointer etc. stuff.
S.th. as simple as that should work:
// file cppcode.hpp
#include<iostream>
class Base
{
public:
virtual void print() { std::cout<< "hello Base"<< std::endl; }
};
class Derived : public Base
{
public:
virtual void print() { std::cout<< "hello Derived"<< std::endl; }
};
// only to show callback-into-python-overrides necessities
void callback(Base& base) {
base.print();
}
// file wrap.cpp
#include<boost/python.hpp>
#include "cppcode.hpp"
namespace bp = boost::python;
BOOST_PYTHON_MODULE(cppcode)
{
bp::class_<Base>("Base")
.def("printIt",&Base::print)
;
bp::class_<Derived, bp::bases<Base> >("Derived");
bp::def("callback",&callback);
};
When run:
# file test.py
import cppcode
derived = cppcode.Derived()
derived.printIt()
cppcode.callback(derived)
class PythonDerived(cppcode.Base):
def printIt(self):
print "hello PythonDerived"
pyderived = PythonDerived()
pyderived.printIt()
cppcode.callback(pyderived)
$ python2.7 -i ./test.py
hello Derived
hello Derived
hello PythonDerived
hello Base
Note that you'd need a Base wrapper class to actually make callbacks to
Python method-overrides work,
just as documented in
http://www.boost.org/doc/libs/1_47_0/libs/python/doc/tutorial/doc/html/python/exposing.html#python.class_virtual_functions
Holger
Landesbank Baden-Wuerttemberg
Anstalt des oeffentlichen Rechts
Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz
HRA 12704
Amtsgericht Stuttgart
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Hi Holger,
thanks for your response.
Ok lets say my BaseClass has a member function called init( vector4 ):
class Base
{
public:
void init( vector4 &vec ) { //doWhatEver }
//a lot of other functions
};
Unfortunetaly i can not expose this init function directly to python so
i am writing a BaseWrapper
class BaseWrapper : public Base, public bp::wrapper<Base>
{
public:
void _init( int first, int second, int third, int fourth) { init(
makeVec(first, second, third, fourth) ); }
// a lot of other wrapper functions
};
And i have a derived class:
class Derived : Base
{
public:
//some more functions
};
So when i am exposing Base and Derived like:
BOOST_PYTHON_MODULE( my_module )
{
class_<Base, BaseWrapper>( "Base", init<>() )
.def("init", &BaseWrapper::_init)
;
class_<Derived, bases<Base> >( "Derived", init<>() );
}
I want to have all functions for objects of Derived that are available
in Base.
The thing is, that e.g. ipython recognizes the functions.
So in ipython, when i have an object of type Derived with tab completion
i see the functions from Base.
But when i try to call them i always get this "signature" error.
So i do not know how to use those callback approach you suggested.
Especially if you are using function overloading. And additionally, this
would mean, that i have to write such a callback function for each
function in my base class as a global function.
I think there is a much simpler way.
One thing i have to mention is, that it is perfectly working if i omit
the BaseWrapper class. So if the functions of Base can be exposed
without using a wrapper class:
class Base
{
public:
void init( int first, int second, int third, int fourth ) {
//doWhatEver }
//a lot of other functions
};
class Derived : public Base
{
};
BOOST_PYTHON_MODULE( my_module )
{
class_<Base>( "Base", init<>() )
.def("init", &Base::init)
;
class_<Derived, bases<Base> >( "Derived", init<>() );
}
In python:
>>derived = my_module.Derived()
>>derived.init(3,1,2,2)
...works. But unfortunately not with the BaseWrapper Class :-(
Sorry for the long post...
Best regards!
--
Erik Türke
Department of Neurophysics
Max-Planck-Institute for Human Cognitive and Brain Sciences
Stephanstrasse 1A
04103 Leipzig
Germany
Tel: +49 341 99 40-2440
Email: [email protected]
www.cbs.mpg.de
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