Re: std::vector member variable as python list

Hi Lars

You could define your own typemaps, but there is quite a lot to override.
Alternatively, add this before the std_vector.i include:

%{
#define SWIG_PYTHON_EXTRA_NATIVE_CONTAINERS
%}

The C++ code then returns a proxy of the std::vector instead of returning a
Python tuple.

William

On Wed, 14 Apr 2021 at 16:48, Lars Jahr Røine <[email protected]> wrote:

> Hi,
>
> I'm using swig to create wrappers for a C++ library. The main class in the
> library has a few public std::vector member variables that I would like to
> access as lists in python. I have simplified my real code to the following
> header file:
>
> example.h
> ---------------
>
> #pragma once#include <vector>#if defined _WIN32
>     #define EXPORT __declspec(dllexport)#else
>     #define EXPORT#endif
> namespace Example {
>     class EXPORT MyClass {
>         public:
>         std::vector<int> my_data{1, 2, 3};
>         std::vector<int> get_vec();
>     };
> }
>
>
> and the closest I have gotten is this (using std_vector.i and %naturalvar
> in my interface file):
>
> >>> from example import MyClass>>> m = MyClass()>>> m.get_vec()
> (1, 3, 5)>>> m.my_data
> (1, 2, 3)>>> m.my_data = [9, 8, 7]>>> m.my_data.append(6)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> AttributeError: 'tuple' object has no attribute 'append'
>
> This is close to  what I want, but since std_vector.i converts
> std::vector to a tuple, it is not possible to append elements to the
> my_data variable. If I remove the %naturalvar from *example.i* I can use
> list methods like append on my_data. However, I then get an error message
> if I try to assign the variable to a python list (since the type of my_data
> then is a proxy of a swig object). I have tried adding a typemap to
> *example.i* file. Then the get_vec method returned a python list, but the
> type of my_data did not change.
>
> %typemap(out) std::vector<int> (PyObject* tmp) %{
>
>     tmp = PyList_New($1.size());
>     for(int i = 0; i < $1.size(); ++i)
>         PyList_SET_ITEM(tmp,i,PyLong_FromLong($1[i]));
>     $result = SWIG_Python_AppendOutput($result,tmp);
> %}
>
>
> After doing some research I suspect that I might need to define
> typemap(in) and typemap(out) for the type const std::vector<int>&, but I
> haven't been able to figure out how they should look. Is creating typemaps
> the way to go for this problem, or would you recomend any other strategies?
> All help is appreciated. Below are all the files needed to build my
> example.
>
> example.i
> -------------
>
> %module example
>
> %include "stdint.i"
> %include "std_vector.i"
>
> %naturalvar;
>
> %{#include <example.h>
> %}
>
> %template(int_vector) std::vector<int>;
> %include <example.h>
>
>
> example.cpp
> -----------------
>
> #include "example.h"
> namespace Example {
>     std::vector<int> MyClass::get_vec() {
>         std::vector<int> v{1, 3, 5};
>         return v;
>     }
> }
>
>
> CMakeLists.txt
> -------------------
>
> cmake_minimum_required(VERSION 3.15)
> project(CMakeSwigExample LANGUAGES CXX)
>
> include_directories(${CMAKE_CURRENT_SOURCE_DIR})
> add_library(example_cpp SHARED example.h example.cpp)
> target_compile_features(example_cpp PUBLIC cxx_std_17)
>
> if (UNIX)
> set_target_properties(example_cpp PROPERTIES INSTALL_RPATH "$ORIGIN")
> endif()
>
> FIND_PACKAGE(SWIG REQUIRED)
> INCLUDE(${SWIG_USE_FILE})
>
> FIND_PACKAGE(PythonLibs)
>
> SET(CMAKE_SWIG_FLAGS "")
>
> SET_SOURCE_FILES_PROPERTIES(example.i PROPERTIES CPLUSPLUS ON)
> set_property(SOURCE itnfileio.i PROPERTY SWIG_MODULE_NAME example)
>
> SWIG_ADD_LIBRARY(example
>     TYPE SHARED
>     LANGUAGE python
>     SOURCES example.i)
>
> target_include_directories(example
>     PRIVATE
>     ${PYTHON_INCLUDE_DIRS})
>
> target_link_libraries(example PRIVATE example_cpp ${PYTHON_LIBRARIES})
>
> Regards,
> Lars
>
>
>
> _______________________________________________
> Swig-user mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/swig-user
>

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