Unexpected floor division with ndarrays on python 3

Build main.cpp được cung cấp bằng CMakeLists.txt đính kèm trong các cấu hình Python 2.7 và 3.6 được liệt kê, sau đó so sánh các kết quả phép chia được in ra. Đọc code liên quan trong examples/ và sử dụng output tái hiện được để xác định liệu hành vi của Python 3 có đúng như dự kiến hay không và liệu có tồn tại một đường dẫn được hỗ trợ cho phép chia không làm tròn xuống hay không; được xem là hoàn thành khi có giải thích được maintainer xác nhận hoặc một fix được xác định chính xác.

Our primarily C++ code base uses an embedded python to do computation with help from boost::python. We are in the process of porting to python 3. We have noticed that it appears that the / operator when acting on a pair of boost::python::numpy::ndarray's yields floor division. That is to say the results are numerically consistent with constructing the same arrays in a python interpreter and then performing arr1 // arr2. We do did not see this behaviour when linking against python27.dll. To make my issue concrete I prepared an example based on those provided in the examples/ folder. It was built on windows 10 using:

• MSVC 2015
• Python 2.7.16
• Python 3.6.8
• cmake 3.16
• Ninja 1.9.0
• Boost 1.70.0

main.cpp was:

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

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

typedef float arr_dtype;

int main(int argc, char **argv)
{
  Py_Initialize();
  np::initialize();

  arr_dtype raw_array1[] = {1.53f, 2.53f, 3.53f, 4.53f};
  np::ndarray nd_array1 = np::from_data(raw_array1, np::dtype::get_builtin<arr_dtype>(),
                                        p::make_tuple(4),
                                        p::make_tuple(4),
                                        p::object());

  arr_dtype raw_array2[] = {0.1f};
  np::ndarray nd_array2 = np::from_data(raw_array2, np::dtype::get_builtin<arr_dtype>(),
                                        p::make_tuple(1),
                                        p::make_tuple(1),
                                        p::object());

  std::cout << "ndarray 1 is " << p::extract<char const *>(p::str(nd_array1)) << std::endl;
  std::cout << "ndarray 2 is " << p::extract<char const *>(p::str(nd_array2)) << std::endl;

  //

  p::object result_array_div = nd_array1 / nd_array2;

  std::cout << "operator/ division of arrays is " << p::extract<char const *>(p::str(result_array_div)) << std::endl;

  return 0;
}

For Python 27 the output when running main.exe was consistent with our expectations:

ndarray 1 is [1.53 2.53 3.53 4.53]
ndarray 2 is [0.1]
operator/ division of arrays is [15.299999 25.3      35.3      45.300003]

For Python 36 the result when running main.exe was not consistent with our (possibly misguided) expectations:

ndarray 1 is [1.53 2.53 3.53 4.53]
ndarray 2 is [0.1]
operator/ division of arrays is [15. 25. 35. 45.]

Is this expected behaviour? Is there any way to enforce non-floor division when using the / operator and python 3?

For reference the CMakeLists.txt was:

cmake_minimum_required(VERSION 3.16)

project(test_boost_numpy_division)

# version selection

if (BUILD_PY3)
   set(python_package_name "Python3")
   set(BOOST_ROOT "${BOOST_ROOT_PY3}")
   set(py_dll_path "${Python3_ROOT_DIR}/python36.dll")
   set(py_maj_min_version "36")
else()
   set(python_package_name "Python2")
   set(BOOST_ROOT "${BOOST_ROOT_PY2}")
   set(py_dll_path "C:/Windows/System32/python27.dll")
   set(py_maj_min_version "27")
endif()

set(boost_python_module_name "python${py_maj_min_version}")
set(boost_numpy_module_name "numpy${py_maj_min_version}")

# python config

find_package (${python_package_name} COMPONENTS Development REQUIRED)

# boost config

set(Boost_USE_MULTITHREADED ON)
set(Boost_USE_STATIC_LIBS OFF)

find_package(Boost REQUIRED COMPONENTS ${boost_python_module_name} ${boost_numpy_module_name} unit_test_framework)

#

add_executable(main)
target_sources(main PRIVATE main.cpp)

target_link_libraries(main ${python_package_name}::Python)
target_link_libraries(main Boost::${boost_python_module_name} Boost::${boost_numpy_module_name})

set_target_properties( main
   PROPERTIES
   ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin"
   RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin"
)

# 

file(COPY "${Boost_LIBRARY_DIRS}/" DESTINATION "${CMAKE_BINARY_DIR}/bin")
file(COPY "${py_dll_path}" DESTINATION "${CMAKE_BINARY_DIR}/bin")