Hello list,
I'm having trouble creating a boost python forward iterator to get a numpy
array as input of a C++ function that takes an stl begin and end iterator
as a template and modifies it, here's the code for the C++ function:
*template<typename _InputIt>*
*void fill_increasing(_InputIt begin, _InputIt end, typename
std::iterator_traits<_InputIt>::value_type start, typename
std::iterator_traits<_InputIt>::value_type increment)*
*{*
* typedef typename std::iterator_traits<_InputIt>::value_type _Type;*
* if (std::is_floating_point<_Type>::value)*
* {*
* std::size_t count = 0;*
* while (begin != end)*
* {*
* *begin = start + ((_Type)count*increment);*
* ++begin;*
* ++count;*
* }*
* }*
* else {*
* while (begin != end)*
* {*
* *begin = start;*
* start += increment;*
* ++begin;*
* }*
* }*
*} *
There is already an implementation of an stl input iterator in Boost Python
(i.e. stl_iterator.hpp) but it's not mutable, so that won't help me here,
so I tried to create my own stl_forward_iterator based on the input
iterator.
*namespace boost {*
* namespace python*
* {*
* // An STL forward iterator over a python sequence*
* template<typename ValueT>*
* struct stl_forward_iterator*
* : boost::iterator_facade<*
* stl_forward_iterator<ValueT>*
* , ValueT*
* , std::forward_iterator_tag*
* >*
* {*
* stl_forward_iterator()*
* : impl_()*
* {*
* }*
* // ob is the python sequence*
* stl_forward_iterator(boost::python::object const &ob)*
* : impl_(ob)*
* {*
* }*
* private:*
* friend class boost::iterator_core_access;*
* void increment()*
* {*
* this->impl_.increment();*
* }*
* ValueT& dereference() const*
* {*
* return extract<ValueT&>(this->impl_.current().get())();*
* }*
* bool equal(stl_forward_iterator<ValueT> const &that) const*
* {*
* return this->impl_.equal(that.impl_);*
* }*
* objects::stl_input_iterator_impl impl_;*
* };*
*}*
*}*
The only change I really made was changing the return of the *deference*
function to a reference instead of just a value.
And I use this in my main application as follows:
*template<typename T>*
*void wrap_fill_increasing(boost::python::numeric::array& array, T start, T
increment) {*
* boost::python::stl_forward_iterator<T> begin(array);*
* boost::python::stl_forward_iterator<T> end;*
* vec_fill_increasing(begin, end, start, increment);*
*}*
*BOOST_PYTHON_MODULE(example) {*
* import_array();*
* p::numeric::array::set_module_and_type("numpy", "ndarray");*
* p::def("fill_increasing", &wrap_fill_increasing<int>);*
*}*
*int main(int argc, char **argv){ PyImport_AppendInittab("example",
&PyInit_example); Py_Initialize(); PyRun_SimpleString(
"import example\n" "import numpy\n" "z3 =
numpy.zeros((1024,), dtype=numpy.int <http://numpy.int>)\n"
"example.fill_increasing(z3, 0, 1)\n" "print(z3)\n" );
Py_Finalize();}*
But I get the error:
*TypeError: No registered converter was able to extract a C++ reference to
type int from this Python object of type numpy.int32*
And it occurs on the *dereference* function in my stl_forward_iterator and
I don't know how to resolve this.
If something that can help he in this scenario doesn't exist, I really
think there should be one as a suggestion.
Any help would be greatly appreciated, thank you.
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