numpy array with swig mapping

Question

I have function which contains 3, one dimension array arguments and one length argument. for example:

float my_func(int *arr1, int *arr2, int *arr3, int length)

This array would be IN_ARRAY and needed to write swig wrapping for it so from the document of the swig, I found

DATA_TYPE IN_ARRAY3[ANY][ANY][ANY]

Is this the right way to do it?

You need pairs int *arr1, int len1 for each of the one-dimensional inputs, if you use the numpy.i file — Jens Munk
– Jens Munk, Commented Oct 23, 2020 at 18:26
@JensMunk Yes, I agree with you and I am aware of it as well. But I have the C function as described here. where only one length parameter is there. — zero cool3
– zero cool3, Commented Oct 26, 2020 at 9:41
Then create in your libraryName.i a C-wrapper function with a signature (int* arr1, int len1, int* arr2, int len2, int* arr3, int len3), which calls your function. Afterwards, you can use the %rename functionality of swig to make the wrapped functions name equal the original name — Jens Munk
– Jens Munk, Commented Oct 26, 2020 at 16:40

Jens Munk · Accepted Answer · 2020-10-26 17:26:52Z

What you can is the following.

zerocool.i

%module zerocool
%{
  #define SWIG_FILE_WITH_INIT
  #include "zerocool.h"
%}

#ifdef SWIGPYTHON
%include "numpy.i"
%init {
  import_array();
 }
#endif

%apply (int* IN_ARRAY1, int DIM1) \
{(int* arr1, int len1)}
%apply (int* IN_ARRAY1, int DIM1) \
{(int* arr2, int len2)}
%apply (int* IN_ARRAY1, int DIM1) \
{(int* arr2, int len2)}

%inline %{
  float my_func(int *arr1, int len1,
                int *arr2, int len2,
                int *arr3, int len3) {
    return my_func(arr1, arr2, arr3, len3);
  }
%}

You original header, say zerocool.h

#pragma once

float my_func(int *arr1, int *arr2, int *arr3, int length);

Your source, say zerocool.cpp

#include "zerocool.h"

#include "stdio.h"

float my_func(int *arr1, int *arr2, int *arr3, int length) {
  printf("Function is called\n");
  // Do some work on your input data
  return 0.0f;
}

Sample CMakeLists.txt file

cmake_minimum_required(VERSION 3.0)

find_package(SWIG REQUIRED)
include(${SWIG_USE_FILE})

set(Python_ADDITIONAL_VERSIONS 3.5 3.6 3.7)
find_package(PythonInterp 3 REQUIRED)
find_package(PythonLibs)

include_directories(${PYTHON_INCLUDE_PATH})
include_directories(${CMAKE_CURRENT_SOURCE_DIR})

set_property(SOURCE zerocool.i PROPERTY SWIG_FLAGS "-D_SWIG_WIN32")
set_source_files_properties(zerocool.i PROPERTIES CPLUSPLUS ON)

swig_add_library(zerocool LANGUAGE python SOURCES zerocool.i zerocool.cpp)
swig_link_libraries(zerocool ${PYTHON_LIBRARIES})

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