Hello,
The topic below was opened in the Boost development mailing list,
where it's been pointed out to me that it fits better here.
You can also read the thread archive:
http://thread.gmane.org/gmane.comp.lib.boost.devel/186573
Regards
Bruno
---------- Forwarded message ----------
Hello,
I have written a little function that converts any Boost.Fusion
sequence into a Python tuple (boost::python::tuple). If a sub-sequence
is nested in the sequence, the result will also be a nested tuple (for
instance, boost::make_tuple(0, std::make_pair(1, 2), 3) will give (0,
(1, 2), 3) in Python).
The source code is attached to this mail.
The principle is that any sequence previously adapted to Boost.Fusion
will become a tuple in Python. So, by including the right
boost/fusion/adapted/xxx header, one can convert a pair, a tuple, a
boost::array, and obviously any of the sequences provided by
Boost.Fusion. For example:
#include <boost/python.hpp>
#include <boost/fusion/adapted/std_pair.hpp>
#include <boost/fusion/adapted/boost_tuple.hpp>
#include <boost/fusion/container/generation/make_vector.hpp>
#include "make_tuple_from_fusion_sequence.hpp"
using namespace boost::python;
tuple from_sequence()
{
return make_tuple_from_fusion(
boost::fusion::make_vector(
1,
std::make_pair("first", "second"),
2,
boost::make_tuple('a', 'b', 'c'),
3
)
);
}
BOOST_PYTHON_MODULE(mymodule)
{
def("from_sequence", &from_sequence);
}
In Python we get:
>>> import mymodule
>>> mymodule.from_sequence()
(1, ('first', 'second'), 2, ('a', 'b', 'c'), 3)
Is there any interest in adding this function into Boost.Python? If
yes, I can write the doc and tests, clean the source and maybe improve
the implementation (for example, I feel that I could avoid the use of
m_iteration with a better use of Boost.Fusion...).
Regards
Bruno
#ifndef BOOST_PYTHON_MAKE_TUPLE_FROM_FUSION_H_
#define BOOST_PYTHON_MAKE_TUPLE_FROM_FUSION_H_
#include <boost/fusion/algorithm/iteration/for_each.hpp>
#include <boost/fusion/include/size.hpp>
#include <boost/fusion/include/is_sequence.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/python/tuple.hpp>
namespace boost {
namespace python {
class tuple_maker
{
public:
tuple_maker(tuple& t):
m_tuple(t),
m_iteration(0)
{}
template <class T>
typename disable_if<fusion::traits::is_sequence<T>, void>::type
operator() (const T& element) const
{ add_element(element); }
template <class Sequence>
typename enable_if<fusion::traits::is_sequence<Sequence>, void>::type
operator() (const Sequence& s) const
{ add_element(make_tuple_from_fusion(s)); }
private:
template <class T>
void add_element(const T& element) const
{
PyTuple_SET_ITEM(
m_tuple.ptr(),
m_iteration++,
incref(object(element).ptr())
);
}
tuple& m_tuple;
mutable int m_iteration;
};
template <class Sequence>
tuple make_tuple_from_fusion(const Sequence& s)
{
tuple result((detail::new_reference)::PyTuple_New(fusion::size(s)));
fusion::for_each(s, tuple_maker(result));
return result;
}
} // namespace python
} // namespace boost
#endif
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