Re: [C++-sig] [boost python] : how to pass a tuple of lists from python to C++

[HOUSSEN Franck]

I tried to play with extract::check() without much success : line 13
crashes !?...
This is a very simple exemple : would like to get it to work. Could
somebody help ? Still googling / searching for a solution

Le ven. 7 févr. 2020 à 22:43, stefan <ste...@seefeld.name> a écrit :

>
> On 2020-02-07 4:06 p.m., HOUSSEN Franck wrote:
>
> With boost python, how to pass a tuple of lists from python to C++ ? Code
> attached : line 12 crashes ?! Googling but no fix for now.
>
> You are referring to this line:
>
>   np::ndarray lsInt = boost::python::extract<np::ndarray>(t[0]);
>
> Note that this line is actually doing two things:
>
> 1) it creates a boost::python::extract<np::ndarray> object
>
> 2) it calls conversion operator on it to convert to np::ndarray
>
> Note that the conversion may fail (for example if the object doesn't
> contain an object of that type). In case of doubt, you may want to call
> extract::check() to see whether it's actually valid.
>
> See
> https://www.boost.org/doc/libs/1_72_0/libs/python/doc/html/reference/to_from_python_type_conversion.html#to_from_python_type_conversion.boost_python_extract_hpp.class_template_extract
> for details.
>
>
>
> [image: Stefan]
>
> --
>
>       ...ich hab' noch einen Koffer in Berlin...
>
>
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-- 
Bonne journée,

Franck HOUSSEN

#include <iostream>

#include <boost/python.hpp>
#include <boost/python/numpy.hpp>

namespace bp = boost::python;
namespace np = boost::python::numpy;

void doStuffs(boost::python::tuple & t) {
  std::cout << "doStuffs" << std::endl;

  boost::python::extract<np::ndarray> lsIntExt(t[0]);
  if (lsIntExt.check()) {
  //  std::cerr << "t[0] is a np::ndarray" << std::endl;
  //  np::ndarray lsInt = lsIntExt(); // Conversion to np::ndarray.
  //  int nbInt = lsInt.shape(0);
  //  std::cout << "nbInt " << nbInt << std::endl;
  //  int * ptrInt = reinterpret_cast<int*>(lsInt.get_data());
  //  std::cout << "ptrInt " << ptrInt << std::endl;
  //  for(auto k = 0; ptrInt && k < nbInt; k++) {std::cout << "ptrInt[" << k << "] = " << ptrInt[k] << std::endl;};
  }
  //else {
  //  std::cerr << "t[0] is not a np::ndarray" << std::endl;
  //}

  //boost::python::extract<np::ndarray> lsFloatExt(t[1]);
  //if (lsFloatExt.check()) {
  //  std::cerr << "t[1] is a np::ndarray" << std::endl;
  //  np::ndarray lsFloat = lsFloatExt(); // Conversion to np::ndarray.
  //  int nbFloat = lsFloat.shape(0);
  //  std::cout << "nbFloat " << nbFloat << std::endl;
  //  float * ptrFloat = reinterpret_cast<float*>(lsFloat.get_data());
  //  std::cout << "ptrFloat " << ptrFloat << std::endl;
  //  for(auto k = 0; k < nbFloat; k++) {std::cout << "ptrFloat[" << k << "] = " << ptrFloat[k] << std::endl;};
  //}
  //else {
  //  std::cerr << "t[1] is not a np::ndarray" << std::endl;
  //}
}

BOOST_PYTHON_MODULE(dummy) {
  def("doStuffs", doStuffs);
}

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