[C++-sig] Cplusplus-sig Digest, Vol 125, Issue 3

[Lewis Evans]

Hello,

I suggest to avoid eval, in main()

instead, after "import test" in main():

funcObj = global["test"].attr("test") // assuming your global["test"] is a
successfully imported module
resultObj = funcObj()

then check resultObj:
as well as extract-and-check, you can query repr/str, and is_none(), and
check attributes __class__ and __class__.__name__

in boost-python say someObject.attr("attributeNameHere")

Best

Lewis




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On Tue, May 12, 2020 at 5:00 PM <cplusplus-sig-request at python.org> wrote:

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> Today's Topics:
>
>    1. Beginner - How to extract a Python Class that inherits from
>       C++ Class (Carlos Duran)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 12 May 2020 12:11:36 +0200
> From: Carlos Duran <carlos_wurt at zohomail.eu>
> To: "cplusplus-sig" <cplusplus-sig at python.org>
> Subject: [C++-sig] Beginner - How to extract a Python Class that
>         inherits from C++ Class
> Message-ID:
>         <172085e498d.e3349fd230005.5688831514627266454 at zohomail.eu>
> Content-Type: text/plain; charset="utf-8"
>
> Hi,
>
>
>
> I was being researching the Boost.Python library, this archive and
> stackoverflow but I couldn't find the correct answer.
>
>
>
> I tried the following:
> -First: I created the C++ Class.
> --------------------------------------------------------------------------
>
> user at host ~/ProjectFolder: cat lib/DemiComponent.hpp
>
> #pragma once
>
> #include <boost/python.hpp>
>
>
>
> namespace DemiWu
>
> {
>
> ?? ?class Component
>
> ?? ?{
>
> ?? ??? ?public:
>
> ?? ??? ?Component(){};
>
> ?? ??? ?virtual ~Component(){};
>
> ?? ??? ?virtual void on_create(){};
>
> ?? ?};
>
>
>
> ?? ?class ComponentWrap : public Component, public
> boost::python::wrapper<Component>
>
> ?? ?{
>
> ?? ??? ?public:
>
> ?? ??? ?void empty(){}
>
> ?? ??? ?virtual void on_create()
>
> ?? ??? ?{
>
> ?? ??? ??? ?this->get_override("on_create")();
>
> ?? ??? ?}
>
> ?? ?};
>
>
>
> ?? ?void import_component()
>
> ?? ?{
>
> ?? ??? ?using namespace DemiWu;
>
> ?? ? ?? ?using namespace boost::python;
>
> ?? ??? ?class_<ComponentWrap, boost::noncopyable>("Component")
>
> ?? ??? ??? ?.def("on_create", &Component::on_create,
> &ComponentWrap::empty);
>
>
>
> ?? ?};
>
> };
>
> --------------------------------------------------------------------------
>
>
>
> -Second: I exported to Python
>
> --------------------------------------------------------------------------
>
> user at host ~/ProjectFolder: cat lib/DemiWu.hpp
>
> #pragma once
>
> #include <boost/python.hpp>
>
> #include <DemiComponent.hpp>
>
>
>
> BOOST_PYTHON_MODULE(DemiWu)
>
> {
>
> ?? ?DemiWu::import_component();
>
> }
>
> --------------------------------------------------------------------------
>
> ?cat lib/DemiWu.cpp
>
> #include <DemiWu.hpp>
>
> ---------------------------
>
>
>
> -Third: I used Meson to compile, but I think that is not important. The
> module works on python3 interpreter.
>
> --------------------------------------------------------------------------
>
>
>
> -Fourth: I wrote a Python Class that inherit form the C++ Class
> DemiWu::Component.
>
> --------------------------------------------------------------------------
>
> user at host ~/ProjectFolder: cat build/test.py
>
> import DemiWu
>
>
>
> class test(DemiWu.Component):
>
> ??? def __init__(self):
>
> ??????? self.x = 10;
>
> ??????? self.y = 20;
>
>
>
> ??? def on_create(self):
>
> ??????? print("(",self.x, ",",self.y,")", sep="")
>
> ??????? self.x = self.x + 1
>
> ??????? self.y = self.y + 1
>
> --------------------------------------------------------------------------
>
>
>
> Fifth: I write a program that extracts the test Python Class.
>
> --------------------------------------------------------------------------
>
> user at host ~/ProjectFolder: cat src/DemiWu.cpp
>
> #include <boost/python.hpp>
>
> #include <DemiComponent.hpp>
>
> #include <DemiWu.hpp>
>
> #include <iostream>
>
> using namespace boost::python;
>
> using namespace DemiWu;
>
>
>
> int main()
>
> {
>
> ?? ?PyImport_AppendInittab("DemiWu", PyInit_DemiWu);
>
> ?? ?Py_Initialize();
>
> ?? ?object main = import("__main__");
>
> ?? ??? ?object global = main.attr("__dict__");
>
> ?? ?PySys_SetPath(L".");
>
> ?? ?global["test"] = import("test");
>
> ?? ?object obj = eval("test.test()", global);
>
> ?? ?extract<Component*> ex(obj);
>
> ?? ?if(ex.check()){
>
> ??? ??? ?Component* b=ex();
>
> ????? ?? b->on_create();?
>
> ?? ??? ? std::cout << "SUCCESS\n";
>
> ?? ??? ? return 0;
>
> ?? ?} else {
>
> ?? ??? ?std::cout << "FAIL\n";
>
> ?? ??? ?return 1;
>
> ?? ?}
>
> }
>
> --------------------------------------------------------------------------
>
>
>
> Sixth: Compile the program successfully.
>
> --------------------------------------------------------------------------
>
>
>
> Seventh: Execute and... the output is always "FAIL".
>
> --------------------------------------------------------------------------
>
>
>
> How can I fix it? What did I miss?
>
>
>
> Thank you for your attention,
>
>
>
> Carlos
>
>
>
> PS: Sorry for the format of the mail, but I can't express on English well.
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>
> End of Cplusplus-sig Digest, Vol 125, Issue 3
> *********************************************
>

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