...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
<boost/python/register_ptr_to_python.hpp>
supplies register_ptr_to_python
, a function template
which registers a conversion for smart pointers to Python. The
resulting Python object holds a copy of the converted smart pointer,
but behaves as though it were a wrapped copy of the pointee. If
the pointee type has virtual functions and the class representing
its dynamic (most-derived) type has been wrapped, the Python object
will be an instance of the wrapper for the most-derived type. More than
one smart pointer type for a pointee's class can be registered.
Note that in order to convert a Python X
object to a
smart_ptr<X>&
(non-const reference), the embedded C++
object must be held by smart_ptr<X>
, and that when wrapped
objects are created by calling the constructor from Python, how they are held
is determined by the HeldType
parameter to
class_<...>
instances.
template <class P> void register_ptr_to_python()
P
is Dereferenceable.
P
instances.
A
with
virtual functions and some functions that work with
boost::shared_ptr<A>
.
struct A { virtual int f() { return 0; } }; shared_ptr<A> New() { return shared_ptr<A>( new A() ); } int Ok( const shared_ptr<A>& a ) { return a->f(); } int Fail( shared_ptr<A>& a ) { return a->f(); } struct A_Wrapper: A { A_Wrapper(PyObject* self_): self(self_) {} int f() { return call_method<int>(self, "f"); } int default_f() { return A::f(); } PyObject* self; }; BOOST_PYTHON_MODULE(register_ptr) { class_<A, A_Wrapper>("A") .def("f", &A::f, &A_Wrapper::default_f) ; def("New", &New); def("Ok", &Call); def("Fail", &Fail); register_ptr_to_python< shared_ptr<A> >(); }
>>> from register_ptr import * >>> a = A() >>> Ok(a) # ok, passed as shared_ptr<A> 0 >>> Fail(a) # passed as shared_ptr<A>&, and was created in Python! Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: bad argument type for built-in operation >>> >>> na = New() # now "na" is actually a shared_ptr<A> >>> Ok(a) 0 >>> Fail(a) 0 >>>If
shared_ptr<A>
is registered as follows:
class_<A, A_Wrapper, shared_ptr<A> >("A") .def("f", &A::f, &A_Wrapper::default_f) ;There will be an error when trying to convert
shared_ptr<A>
to
shared_ptr<A_Wrapper>
:
>>> a = New() Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: No to_python (by-value) converter found for C++ type: class boost::shared_ptr<struct A> >>>
Revised 24 Jun, 2003
© Copyright Dave Abrahams 2002.