I am using Boost.Python to expose a 3rd party C++ API.
A header file I've come to declares an iterable class (has begin and end methods), and a custom iterator class with which to do the iteration:-
// File: data.hpp
#include <utility> // for std::pair
#include <cstring> // for size_t
namespace notmylib {
// forward declaration
class DataIterator;
// Storage for arbitrary data
class Data
{
public:
Data(void);
virtual ~Data(void);
// ...
typedef DataIterator const_iterator;
const_iterator begin(void) const;
const_iterator end(void) const;
typedef std::pair<int, int> TRange;
private:
TRange m_data;
};
// Data iterator class
class DataIterator
{
public:
// constructors
DataIterator(void);
DataIterator(const Data);
~DataIterator(void);
// copy constructor
DataIterator(const DataIterator& iter);
// assignment operator
DataIterator& operator=(const DataIterator& iter);
// Comparison operators
bool operator==(const DataIterator& iter) const;
bool operator!=(const DataIterator& iter) const;
// Data Range
typedef TData::TRange TRange;
TRange GetRange(void) const;
Data GetRangeAsData(void) const;
// Go backwards one step
void Rewind(void);
private:
Data m_data;
size_t m_index;
};
}
I've created minimal wrapper classes deriving from these:-
// File: pydata.hpp
#include "data.hpp"
namespace mylib {
class PyData
: public notmylib::Data
{
public:
PyData(void);
virtual ~PyData(void);
};
class PyIterator
: public notmylib::DataIterator
{
public:
PyIterator(void);
PyIterator(const notmylib::Data);
PyIterator(const PyIterator& iter);
~PyIterator(void);
};
}
And the Boost.Python declaration:-
// File: pydata.cpp
#include "pydata.hpp"
#include <boost/python/class.hpp>
#include <boost/python/iterator.hpp>
#include <boost/python/module.hpp>
BOOST_PYTHON_MODULE(const_iterator)
{
using namespace boost::python;
class_<mylib::PyData, boost::noncopyable>("Data",
"Iterable Data storage class.")
.def("__iter__",
iterator<const mylib::PyData>() /*, // */ ) ///< iterator / range / iterators ?
// boost::python::return_value_policy< ///< This CallPolicy
// boost::python::copy_const_reference> >() ) /// doesn't work either
;
class_<mylib::PyIterator>("DataIterator",
"Iterator for Data class. Don't actually need to expose...")
.def("__eq__", &mylib::PyIterator::operator==)
.def("__neq__", &mylib::PyIterator::operator!=)
// ...
;
}
The only oddity here seems to be the use of the const_iterator typedef. This is described in the Boost.Python iterator documentation, and from what I gather, all that it needs is a const qualifier in iterator's template parameters. i.e.
boost::python::iterator<const mylib::PyData>()
However, that leads to the following compiler error, using GCC 4.7.2 on Linux x86_64:-
g++ -std=gnu++98 -c -g -O1 -fPIC -I/usr/include/python2.7 pydata.cpp -o pydata.o
In file included from /usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/stl_algobase.h:66:0,
from /usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/memory:64,
from /usr/include/boost/config/no_tr1/memory.hpp:21,
from /usr/include/boost/get_pointer.hpp:14,
from /usr/include/boost/python/object/pointer_holder.hpp:11,
from /usr/include/boost/python/to_python_indirect.hpp:10,
from /usr/include/boost/python/converter/arg_to_python.hpp:10,
from /usr/include/boost/python/call.hpp:15,
from /usr/include/boost/python/object_core.hpp:14,
from /usr/include/boost/python/object/class.hpp:9,
from /usr/include/boost/python/class.hpp:13,
from pydata.cpp:4:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/stl_iterator_base_types.h: In instantiation of 'struct std::iterator_traits<notmylib::DataIterator>':
/usr/include/boost/detail/iterator.hpp:81:8: required from 'struct boost::detail::iterator_traits<notmylib::DataIterator>'
/usr/include/boost/python/object/iterator.hpp:58:17: required from 'struct boost::python::objects::iterator_range<boost::python::return_value_policy<boost::python::return_by_value>, notmylib::DataIterator>::next'
/usr/include/boost/python/object/iterator.hpp:127:45: required from 'boost::python::api::object boost::python::objects::detail::demand_iterator_class(const char*, Iterator*, const NextPolicies&) [with Iterator = notmylib::DataIterator; NextPolicies = boost::python::return_value_policy<boost::python::return_by_value>]'
/usr/include/boost/python/object/iterator.hpp:167:11: required from 'boost::python::objects::iterator_range<NextPolicies, Iterator> boost::python::objects::detail::py_iter_<Target, Iterator, Accessor1, Accessor2, NextPolicies>::operator()(boost::python::back_reference<Target&>) const [with Target = const mylib::PyData; Iterator = notmylib::DataIterator; Accessor1 = boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >; Accessor2 = boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >; NextPolicies = boost::python::return_value_policy<boost::python::return_by_value>]'
/usr/include/boost/python/detail/invoke.hpp:75:82: required from 'PyObject* boost::python::detail::invoke(boost::python::detail::invoke_tag_<false, false>, const RC&, F&, AC0&) [with RC = boost::python::to_python_value<const boost::python::objects::iterator_range<boost::python::return_value_policy<boost::python::return_by_value>, notmylib::DataIterator>&>; F = boost::python::objects::detail::py_iter_<const mylib::PyData, notmylib::DataIterator, boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >, boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >, boost::python::return_value_policy<boost::python::return_by_value> >; AC0 = boost::python::arg_from_python<boost::python::back_reference<const mylib::PyData&> >; PyObject = _object]'
/usr/include/boost/python/detail/caller.hpp:223:13: required from 'PyObject* boost::python::detail::caller_arity<1u>::impl<F, Policies, Sig>::operator()(PyObject*, PyObject*) [with F = boost::python::objects::detail::py_iter_<const mylib::PyData, notmylib::DataIterator, boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >, boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >, boost::python::return_value_policy<boost::python::return_by_value> >; Policies = boost::python::default_call_policies; Sig = boost::mpl::vector2<boost::python::objects::iterator_range<boost::python::return_value_policy<boost::python::return_by_value>, notmylib::DataIterator>, boost::python::back_reference<const mylib::PyData&> >; PyObject = _object]'
/usr/include/boost/python/object/py_function.hpp:38:33: required from 'PyObject* boost::python::objects::caller_py_function_impl<Caller>::operator()(PyObject*, PyObject*) [with Caller = boost::python::detail::caller<boost::python::objects::detail::py_iter_<const mylib::PyData, notmylib::DataIterator, boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >, boost::_bi::protected_bind_t<boost::_bi::bind_t<notmylib::DataIterator, notmylib::DataIterator (*)(const mylib::PyData&), boost::_bi::list1<boost::arg<1> > > >, boost::python::return_value_policy<boost::python::return_by_value> >, boost::python::default_call_policies, boost::mpl::vector2<boost::python::objects::iterator_range<boost::python::return_value_policy<boost::python::return_by_value>, notmylib::DataIterator>, boost::python::back_reference<const mylib::PyData&> > >; PyObject = _object]'
pydata.cpp:26:1: required from here
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/stl_iterator_base_types.h:166:53: error: no type named 'iterator_category' in 'class notmylib::DataIterator'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/stl_iterator_base_types.h:167:53: error: no type named 'value_type' in 'class notmylib::DataIterator'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/stl_iterator_base_types.h:168:53: error: no type named 'difference_type' in 'class notmylib::DataIterator'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/stl_iterator_base_types.h:169:53: error: no type named 'pointer' in 'class notmylib::DataIterator'
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/stl_iterator_base_types.h:170:53: error: no type named 'reference' in 'class notmylib::DataIterator'
How should such an iterable class be exposed?
Cheers, Alex
