1962
Comment:
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1977
fixed grammar mistakes and made more readable
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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. | Since Python handles memory allocation and garbage collection automatically, the concept of a "pointer" is not meaningful in Python. However, many C++ APIs expose either raw pointers or shared pointers, to wrap these APIs we need to deal with pointers. |
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=== Pointers (raw C++ pointers) === | === Raw C++ Pointers === |
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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: | The lifetime of C++ objects created by {{{new A}}} can be handled by Python's garbage collection by using the {{{manage_new_object}}} return policy: |
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{{{struct A { | {{{ struct A { |
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.def("create",&A::create,return_value_policy<manage_new_object>()) | .def("create",&A::create, return_value_policy<manage_new_object>()) |
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print A.hello() | print an_A.hello() |
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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()}}}: |
The usage of smart pointers (e.g. {{{boost::shared_ptr<T>}}}) is another common way to give away ownership of objects in C++. These kinds of smart pointer are automatically handled if you declare their existence when declaring the class to boost::python. This is done by including the holding type as a template parameter to {{{class_<>}}}, like in the following example: |
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{{{#include <boost/shared_ptr.h> | {{{ #include <string> #include <boost/shared_ptr.hpp> #include <boost/python.hpp> |
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using namespace std; using namespace boost::python; |
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shared_ptr<A> create () { return shared_ptr<A>(new A); } std::string hello () { return "Just nod if you can hear me!"; } |
static shared_ptr<A> create () { return shared_ptr<A>(new A); } std::string hello () { return "Just nod if you can hear me!"; } |
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class_<A>("A",init<>()) .def("create",&A::create,return_value_policy<return_by_value>()) |
class_<A, shared_ptr<A> >("A",init<>()) .def("create",&A::create ) |
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; class_< shared_ptr<A> >("A_ptr", init<const shared_ptr<A>& >()) .def("__pos__",&boost::shared_ptr<A>::get,return_internal_reference<>()) ; |
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an_A = A_ptr.create() print (+an_A).hello() |
an_A = A.create() print an_A.hello() |
Pointers and smart pointers
Since Python handles memory allocation and garbage collection automatically, the concept of a "pointer" is not meaningful in Python. However, many C++ APIs expose either raw pointers or shared pointers, to wrap these APIs we need to deal with pointers.
Raw C++ Pointers
The lifetime of C++ objects created by new A can be handled by Python's garbage collection by using the manage_new_object return 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
The usage of smart pointers (e.g. boost::shared_ptr<T>) is another common way to give away ownership of objects in C++. These kinds of smart pointer are automatically handled if you declare their existence when declaring the class to boost::python. This is done by including the holding type as a template parameter to class_<>, like in the following example:
#include <string> #include <boost/shared_ptr.hpp> #include <boost/python.hpp> using namespace boost; using namespace std; using namespace boost::python; 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()