Re: Conversion of Python list to class that takes a vector in a constructor

Take a look at %implicitconv mentioned in the CHANGES file
http://swig.org/Release/CHANGES

I think this should work:

%implicitconv S;

William

On Mon, 25 Oct 2021 at 13:30, Lluís Alemany Puig <[email protected]>
wrote:

> Hello all,
>
> I have a C++ class S which takes a std::vector<int> as only input
> parameter in one of its constructors. I can create an object of S
> normally from Python using its constructor passing to it a python list (
> [1,2,3,...]). However, I can't call the function calculate_sum (which
> takes a const S&) when I pass to it a python list instead an object of
> type S. To be more precise, in the following python code, the print("3:",
> ...)
>
> import library
> print("1:", library.return_pair(10))
> d = library.D()
> d.v = 3
> print("2:", library.calculate_sum(d, library.S([1,2,3,4])))
> print("3:", library.calculate_sum(d, [1,2,3,4]))
>
> fails with the expected error message:
>
> Traceback (most recent call last):
>   File "test.py", line 6, in <module>
>     print(library.calculate_sum(d, [1,2,3,4]))
>   File "library.py", line 261, in calculate_sum
>     return _library.calculate_sum(d, s)
> TypeError: in method 'calculate_sum', argument 2 of type 'S const &'
>
> I'm trying to overcome this problem. That is, I would like python to
> create an object of type S given that it has a constructor with a vector
> (C++ code at the end). Can this be done? If so, how? I tried typemaps but I
> don't seem to be able to get them working for this.
>
> Many thanks in advance.
>
> Looking forward to hearing from you,
>
> Lluís.
>
> C++ code:
>
> #pragma once
> #include <vector>
> class D {
> public:
>     int v;
> };
>
> class S {
> public:
>     S() noexcept = default;
>     S(const std::vector<int>& _v) noexcept : v(_v) {}
>     int elemsum() const noexcept {
>         int s = 0;
>         for (int k : v) { s += k; }
>         return s;
>     }
> private:
>     std::vector<int> v;
> };
>
> int calculate_sum(const D& d, const S& s) { return s.elemsum() + d.v; }
> std::pair<int, S> return_pair(int v) {
>     S s(std::vector<int>(v,v));
>     return {s.elemsum(), s};
> }
>
> Interface file (.i):
>
> %module library
>
> %include stdint.i
> %include std_string.i
> %include std_pair.i
> %include std_vector.i
>
> %template(_list_int) std::vector<int>;
>
> %{
> #include <sstream>
> #include "library.hpp"
> %}
>
> %include library.hpp
>
> %extend S {
>     std::string __repr__() const {
>         std::ostringstream out;
>         out << "I am a simple 'S'";
>         return out.str();
>     }
> }
>
> %template(_pair_int_S) std::pair<int, S>;
>
> Makefile:
>
> _library.so: library.o
>     g++ -shared -O3 -o _library.so library.o -L /usr/lib/x86_64-linux-gnu/
> -lpython3.8
> library.o: library.cxx
>     g++ -fPIC -std=c++17 -O3 -c library.cxx -I /usr/include/python3.8
> library.cxx: library.i library.hpp
>     swig -Wall -debug-tmused -c++ -python -py3 -o library.cxx library.i
> clean:
>     rm -f library.cxx
>     rm -f library.py
>     rm -f library.o
>     rm -f _library.so
>
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>

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