Re: [Boost-users] [python] Extending: Understanding ownership of pointers

From: Per Ghosh (per_at_[hidden])
Date: 2008-03-25 07:33:06

As I understand it (been working with boost-python for two weeks) so:

returning a pointer by 
"return_value_policy<reference_existing_object>()" and that
pointer will not be managed by python (not deleted)

returning a pointer by 
"return_value_policy<manage_new_object>()" and that
pointer will be managed by python. It will be deleted by python.

I order to return a pointer to python, the pointer should point to a
known object (declared within the BOOST_PYTHON_MODULE macro)


Robert Dailey skrev:
> Hi,
>   
> I had a bit of trouble deciding which mailing list to post this
> question (Python or boost). I decided to post it here since the way I'm
> extending is boost-specific, however the fundamental question is in
> regards to how Python internally handles ownership. I do not feel there
> is a perfect location for this question, so I hope you'll forgive the
> semi-off topicness of the question.
>   
> Right now I'm exposing a function to Python that returns a pointer to a
> custom object owned by a third party library. In most cases I can
> manage to use boost::shared_ptr when I'm returning pointers, however
> since this is a third party library I cannot do this. Since the pointer
> I'm returning is owned and managed by another object, I gave my def()
> the following return policy:
>   
> return_value_policy<reference_existing_object>()
>   
> I simply assumed this was correct. How does Python handle the pointer
> to this object? Is there some documents in either boost or the python
> documentation that I can read to understand a little more about how
> Python handles object ownership when the Python objects really
> represent C++ pointers? Perhaps someone could give me a brief rundown
> on the concept.
>   
> Thanks in advance.
>
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