On 20/05/2010, at 11:03 PM, Kun Hong wrote:
Hi,
I have a maybe entry-level question. But it really troubled me for a
while.
I need to wrap a C++ library which has some factory method to return
references to some abstract base classes. So the implementation is
hidden. If I want a python equivalent to the abstract base class
reference type
(so the polymorphism can work), how should I do it?
Please see a very simplified example below which demonstrates what I
mean.
Finally, I get to understand it and be able to answer my own question.
Post my own answer so future reader can get a pointer directly.
The answer is in the test code that comes with boost python library.
The code is in libs/python/test/polymorphism.{cpp,py}
I got my code working like below:
========== test.cpp ==========
#include <boost/python.hpp>
using namespace boost::python;
class B
{
public:
virtual const char *getName() const = 0;
virtual int getValue() const
{
return 10;
}
};
class C : public B
{
public:
virtual const char *getName() const
{
return "Class C";
}
};
struct BWrap : public B
{
BWrap(PyObject *self) : mSelf(self) {}
PyObject *mSelf;
const char *getName() const
{
return call_method<const char *>(mSelf, "getName");
}
};
const B &getB()
{
static boost::shared_ptr<B> b(new C);
return (*b.get());
}
BOOST_PYTHON_MODULE(Test)
{
class_<B, BWrap, boost::noncopyable> ("B", no_init)
.def("getName", pure_virtual(&B::getName))
.def("getValue", &B::getValue)
;
class_<C, bases<B> >("C")
.def("getName", &C::getName)
;
def("getB", &getB,
return_value_policy<reference_existing_object>());
}
======== test.py =========
from Test import *
print getB().getName()
print getB().getValue()
c = C()
print c.getName()
print c.getValue()
#b = B()
#print b.getName()
#print b.getValue()
=== end
Not fully understand the pure_virtual call though, which doesn't
prevent B
instance be created in python. "no_init" is needed for preventing B
creation.
But, fun learning boost python, a lot to learn.
Kun
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