[C++-sig] Re: instantiating python objects within C++

[Ralf W. Grosse-Kunstleve]

--- Stefan Seefeld <seefeld at sympatico.ca> wrote:
> David Abrahams wrote:
> 
> > The Boost.Python shared library has a converter registry where all of
> > this information is stored.
> 
> ok, this seems really to be the key. How does this work ? I'm a bit confused,
> as conceptually the lines
> 
> BOOST_PYTHON_MODULE(Sandbox)
> {
>    python::class_<Base> base_type("Base");
>    //...
> }
> 
> create a type 'Sandbox.Base', i.e. the equivalent in C++ would be
> something like 'Sandbox::Base'. However, 'Sandbox' isn't a type,
> so I wonder how I can access the above type object from inside
> C++.

I cannot conclusively answer all your questions, but maybe I can help with one
piece of the puzzle: the central Boost.Python type conversion registry is *not*
scoped. It knows about your type only as, e.g., namespace1::namespace2::base.
If I understand correctly the class_<> constructor does two more or less
independent things (at runtime):

1. It registers the type conversions in the central registry with the C++ type
(in some form) as the key.

2. It adds a reference to the Python type (created at compile time!) to the
current scope().

I am sure the exact details are more involved and my view is maybe not 100%
accurate, but the mental model works for me.

Ralf


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