[C++-sig] boost::python constructing object from PyObject *

[David Abrahams]

on Wed Oct 29 2008, Hans Meine <hans_meine-AT-gmx.net> wrote:

> On Mittwoch 29 Oktober 2008, David Abrahams wrote:
>> The above should be a complete guide.  Any questions?
>
> Great, thanks a lot for the write-up.  I think my second question is still 
> left, at least from your post and the docs at
> http://www.boost.org/doc/libs/1_36_0/libs/python/doc/v2/handle.html
> I have the impression that a handle<> can only be created from PyObject-style 
> pointers.  

Only from a pointer whose target's initial members are layout-compatible
with PyObject, to be precise.

> So, let's say I have exported a class Foo, and I write a wrapper 
> for a factory function that creates a new Foo, and wants to convert it to 
> python in order to manually add some attributes (cf. my deep_copy 
> implementation).  Is there a better way than the following for creating 
> result from new_foo?
>
> Foo *new_foo = new Foo(...);
> bp::object result =
>   bp::detail::new_reference(
>     typename manage_new_object::apply<Foo *>::type()(new_foo);
> result.attr("bar") = 42;
> return result;

Either of these works:

  boost::shared_ptr<Foo> px(new Foo(...));
  object result(px);
  result.attr("bar") = 42;
  return result;

or:

  class_<Foo, ...> py_foo(...);
  py_foo.def(...)
        .def(...)
        ;

    ...
  
  object result = py_foo( ... );
  result.attr("bar") = 42;
  return result;
  
-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com