troy d. straszheim wrote:
>  Thomas Daniel wrote:
> >
> > BOOST_PYTHON_MODULE(vegetables)
> > {
> >    class_<Garden>("Garden")
> >        .def("get_potatoes", &Garden::get_potatoes)
> >        .def("get_tomatoes", &Garden::get_tomatoes)
> >    ;
> >    class_<TomatoIter>("TomatoIter")
> >        .def("__iter__", &TomatoIter::get_next)
> >    ;
> > }
> >
> > That at least compiles - unlike all my previous attempts that 
> > generate three pages of template errors - but python complain:
> >
> > TypeError: iter() returned non-iterator of type 'Tomato'
> >
> > so now I am trying to figure out how to tell boost that get_tomatoes 
> > returns an iterator ...
> >
> 
>  Please don't top-post, guys
> 
>  As you know, python iterators have a function next() that returns the 
>  next object in the iteree, or throw StopIteration when they're at the 
>  end.  As you also know, python expects member functions __iter__() to 
>  return an iterator.  Is the thing returned by TomatoIter::get_next an 
>  iterator, ie does it implement the iterator interface?
> 
>  -t
> 
> 
Thank you very much for the email, you did put me on the right track and 
I finally figured out how to do it, with help from here also: 
http://wiki.python.org/moin/boost.python/iterator

The solution involves creating a wrapper class around get_next(), which 
throws StopIteration when done and a "pass_through" function to bind to 
__iter__:

inline TomatoIter pass_through(const TomatoIter& iter) { return iter; }

Tomato next(TomatoIter& iter) {
    Tomato tomato = iter.get_next();
    if (!tomato) {
        PyErr_SetString(PyExc_StopIteration, "No more data.");
        throw_error_already_set();
    }
    return tomato;
}

Now, I can do this:
BOOST_PYTHON_MODULE(Garden)
{  
     ......
    class_<TomatoIter> ("TomatoIter", no_init)
        .def("next", next)
        .def("__iter__", pass_through)
    ;

and it works.

Thomas

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