Fwd: [boost-python] Making a reference to the PyObject* in construct()

[Austin Bingham]

I'm trying to figure out an issue that seems to have to do with the
construct() method in a from-python conversion. I'm converting from a
python string to a custom C++ string class. The c++ string just holds
a reference to a python string using a boost::python::object. My
construct() function looks like this:

 struct String_from_python_str
 {
   . . .
   static void construct(
     PyObject* obj_ptr,
     boost::python::converter::rvalue_from_python_stage1_data* data)
     {
       using namespace boost::python;

       void* storage = (
           (converter::rvalue_from_python_storage<String>*)
            data)->storage.bytes;
         new (storage) String(object(handle<>(obj_ptr)));  // <---- Is
this correct? Should it be borrowed?
         data->convertible = storage;
     }
 };

My program has started seeing occasional python reference counting
problems and what appear to be memory corruption problems. I find that
if I use a borrowed() handle when constructing my string, the problems
go away. Is this correct? Or am I doing something totally else wrong
here?

I can't find any documentation re: the "borrowed" nature of obj_ptr,
so I really just assumed that it was a normal, pre-incremented
reference. Any help on this would be great. Thanks.

Austin Bingham
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[troy d. straszheim]

Austin Bingham wrote:
>
> I can't find any documentation re: the "borrowed" nature of obj_ptr,
> so I really just assumed that it was a normal, pre-incremented
> reference. Any help on this would be great. Thanks.
>

Here's a good thread on this, thanks to Alex Mohr:

http://mail.python.org/pipermail/cplusplus-sig/2009-February/014294.html

-t



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[Austin Bingham]

Thanks for the link, but I think I misspoke a bit. I do understand
borrowed vs. owned references in general, but I'm not sure about the
pointer in the specific context of the construct() call. Is it
borrowed or pre-incremented?

However, a little poking around the boost.python source seems to
indicate that it the pointers in that context are borrowed. The
evidence I have is that boost.python's own shared_ptr converter,
python/converter/shared_ptr_from_python.hpp, is using 'borrowed' when
it forms a reference to the PyObject.

So, can anyone verify that this is correct?

Austin

On Sat, Sep 26, 2009 at 6:07 PM, troy d. straszheim <troy@...> wrote:

> Austin Bingham wrote:
>>
>> I can't find any documentation re: the "borrowed" nature of obj_ptr,
>> so I really just assumed that it was a normal, pre-incremented
>> reference. Any help on this would be great. Thanks.
>>
>
> Here's a good thread on this, thanks to Alex Mohr:
>
> http://mail.python.org/pipermail/cplusplus-sig/2009-February/014294.html
>
> -t
>
>
>
> _______________________________________________
> Cplusplus-sig mailing list
> Cplusplus-sig@...
> http://mail.python.org/mailman/listinfo/cplusplus-sig
>

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