Pointers and smart pointers

Since Python handles memory allocation and garbage collection automatically, the concept "pointer" is not meaningful within Python. However, many C++ API exposes either raw pointers or shared pointers, and to wrap such APIs one would need to deal with pointers.

Pointers (raw C++ pointers)

The life time of C++ objects created by "new A" can be handled by Python's garbage collection by using the manage_new_object storage policy:

struct A {
    static A*   create () { return new A; }
    std::string hello  () { return "Hello, is there anybody in there?"; }
};

BOOST_PYTHON_MODULE(shared_ptr)
{
    class_<A>("A",no_init)
        .def("create",&A::create,return_value_policy<manage_new_object>())
        .staticmethod("create")
        .def("hello",&A::hello)
        ;
}

A sample python program:

from pointer import *
an_A = A.create()
print an_A.hello()

Smart pointers

Smart pointers, e.g. boost::shared_ptr<T>, is another common way to give away ownership of objects in C++. Theese kind of smart pointer are automatically handled, if you declare their existence, when declaring the class to boost.python.

E.g.

{{{#include <boost/shared_ptr.h> using namespace boost;

struct A {

• static shared_ptr<A> create () { return shared_ptr<A>(new A); } std::string hello () { return "Just nod if you can hear me!"; }

};

BOOST_PYTHON_MODULE(shared_ptr) {

• class_<A, shared_ptr<A> >("A",init<>())

  • def("create",&A::create )

  • staticmethod("create")

  • def("hello",&A::hello)

  ;

} }}}

A sample python program:

from shared_ptr import *
an_A = A.create()
print an_A.hello()