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" kan be handled by Pythons 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++. The following suggests a way to handle shared_ptr objects in Python, introducing the notation (+ptr).foo() in python to immitate C++'s (*ptr).foo():

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

struct A {

• 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>("A",init<>())

  • def("create",&A::create,return_value_policy<return_by_value>())

  • staticmethod("create")

  • def("hello",&A::hello) ;

  class_< shared_ptr<A> >("A_ptr", init<const shared_ptr<A>& >())

  • def("pos",&boost::shared_ptr<A>::get,return_internal_reference<>()) ;

} }}}

A sample python program:

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