Hi,
> 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
Why's that? Can't you expose vector4 to Python?
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.
I think the problem is that the Derived class doesn't actually have any
inheritance
relationship with BaseWrapper, i.e.
Base
/ \
/ \
/ \
BaseWrapper Derived
So in an example like this
// file cppcode.hpp
#include<iostream>
class Base
{
protected:
int m_area;
public:
Base() : m_area(0) {}
void init(int area) {
m_area = area;
}
virtual void print() { std::cout<< "hello Base "<< m_area<<
std::endl; }
};
class Derived : public Base
{
public:
virtual void print() { std::cout<< "hello Derived "<< m_area<<
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;
class BaseWrapper : public Base, public bp::wrapper<Base>
{
public:
void _init(int x, int y) {
init(x * y);
}
};
BOOST_PYTHON_MODULE(cppcode)
{
bp::class_<BaseWrapper, boost::noncopyable>("Base")
.def("init",&BaseWrapper::_init)
.def("printIt",&Base::print)
;
bp::class_<Derived, bp::bases<Base> >("Derived");
bp::def("callback",&callback);
};
#!/apps/local/gcc/4.5.1/bin/python2.7
# file test.py
import cppcode
print "---> base"
base = cppcode.Base()
base.printIt()
base.init(3, 4)
base.printIt()
print "---> derived"
derived = cppcode.Derived()
derived.printIt()
derived.init(3, 4)
derived.printIt()
cppcode.callback(derived)
class PythonDerived(cppcode.Base):
def printIt(self):
print "hello PythonDerived"
print "---> python derived"
pyderived = PythonDerived()
pyderived.printIt()
cppcode.callback(pyderived)
I run into this error when trying to call .init() on the Derived object:
$ python2.7 ./test.py
---> base
hello Base 0
hello Base 12
---> derived
hello Derived 0
Traceback (most recent call last):
File "./test.py", line 23, in<module>
derived.init(3, 4)
Boost.Python.ArgumentError: Python argument types in
Base.init(Derived, int, int)
did not match C++ signature:
init(BaseWrapper {lvalue}, int, int)
Which makes sense since Derived does not inherit from BaseWrapper.
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.
Never mind the callback, I might have just confused you. The callback is
only for showing
that you'd need a Wrapper class if you want to inherit in Python and be
able to call back
from C++ into Python and actually call methods overridden in Python.
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:
[...]
...works. But unfortunately not with the BaseWrapper Class :-(
Because now you don't have the problem that Derived has no inheritance
relationship with BaseWrapper.
Maybe you can just use a free function:
// file wrap.cpp
#include<boost/python.hpp>
#include "cppcode.hpp"
namespace bp = boost::python;
void _init(Base& base, int x, int y) {
base.init(x * y);
}
BOOST_PYTHON_MODULE(cppcode)
{
bp::class_<Base>("Base")
.def("init",&_init)
.def("printIt",&Base::print)
;
bp::class_<Derived, bp::bases<Base> >("Derived");
bp::def("callback",&callback);
};
# file test.py
import os
import sys
import cppcode
print "---> base"
base = cppcode.Base()
base.printIt()
base.init(3, 4)
base.printIt()
print "---> derived"
derived = cppcode.Derived()
derived.printIt()
derived.init(3, 4)
derived.printIt()
cppcode.callback(derived)
class PythonDerived(cppcode.Base):
def printIt(self):
print "hello PythonDerived"
print "---> python derived"
pyderived = PythonDerived()
pyderived.printIt()
# to make this invoke PythonDerived.printIt() you need a wrapper class
cppcode.callback(pyderived)
===>
$ python2.7 ./test.py
---> base
hello Base 0
hello Base 12
---> derived
hello Derived 0
hello Derived 12
hello Derived 12
---> python derived
hello PythonDerived
hello Base 0
Holger
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