Re: export with PyCXX

[Barry S. <ba...@ba...>]

> On 9 Nov 2019, at 20:18, Anton Milev <am...@ab...> wrote:
> 
> Hello, Bary.
> 
> Thanks! I will risk to ask for some improvements even if I do not understand completely PyCXX. I will happy if you answer any of it 
> 
> 1. Can you add a VS2017/19  Step-by-Step demo? I actually started using PyCXX with VS2017 so if you like I can help with this.

Sorry I'm not a Visual Studio GUI user. I use the VS C++ from the command line.

> 2. With VS 2017 I had to search for and add all .cxx files from "C:\PyCXX\Src"  (cxx_extensions.cxx,. ...) to the VS project. This is not convenient.

> Is it possible to create with the build scripts a single  lib file and I to include in my project only the libs path (from Linker > General->Additional Library Directories) ?

It is not practical to provide as a lib.
This is because you have to compile the code with the C++ options that you have chosen for the rest of your project.
For example some projects want RTTI and others do not.
You might use Python limiter API or not.

> It is similar to how Python libs are included in VS, you only include <Python.h> and set the link path.

> 3. I am confused with the demos, simple.cxx is not simple at all and is hard for me to start using it.

Simple is relative...

What I mean by simple is that its shows the simplest way to create a module, class and function, etc.

> Please advice me in the following case - 
> 
> I have a C++ class A. It is quite complicated and contains a lot of functions and code. I want to export this class A to Python. 
> 
> Is this the right approach:
> 
> class OldClass: public Py::PythonExtension< OldClass >
> 
> 

Look at Demo/Python3/simple.cxx and follow the pattern of the new_style_class.
You are using the older style of classes that is not recommended for new code.

> {
> 
> public:
> 
>     OldClass()
> 
>     {
> 
>     }
> 
>  
>     virtual ~OldClass()
> 
>     {
> 
>     }
> 
>  
>     static void init_type(void)
> 
>     {
> 
>         behaviors().name("simple.OldClass");
> 
>         behaviors().doc("documentation for OldClass class");
> 
>         behaviors().supportGetattr();
> 
>  
>         add_noargs_method("func1",&OldClass::func1);
> 
>         add_varargs_method("func2",&OldClass::func2);
> 
>         add_keyword_method("func3",&OldClass::func3);
> 
>  
>         behaviors().readyType();
> 
>     }
> 
>  
>     // override functions from PythonExtension
> 
>     virtual Py::Object getattr(const char *name)
> 
>     {
> 
>         return getattr_methods(name);
> 
>     }
> 
>  
>     Py::Object func1(void)
> 
>     {
> 
>         std::cout << "func1 Called." << std::endl;
> 
>         return Py::None();
> 
>     }
> 
>  
>     Py::Object func2(const Py::Tuple &args)
> 
>     {
> 
>         std::cout << "func2 Called with " << args.length() << " normal arguments." << std::endl;
> 
>         return Py::None();
> 
>     }
> 
>      
>     
> private:
> 
> CppClass m_cpp ;
> 
> };
> 
> 4. I have in my class A many overload operators and I want to use them in Python too.
> 
> For example:
> 
> >>> import simple
> >>> a = simple.OldClass()
> >>> a.func1()
> func1 Called.
> >>> a.func2(5)
> func2 Called with 1 normal arguments.
> >>> b = a
> 
> So far Ok but how to do with PyCXX support the following operators:
> 
> 
> >>> b += a
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: unsupported operand type(s) for +=: 'simple.OldClass' and 'simple.OldClass'

You have to implement the number_inplace_add. See Demo/Python3/simple.cxx 
(I just added support for inplace add today. Please get check out the source:

svn co https://svn.code.sf.net/p/cxx/code/trunk/CXX <https://svn.code.sf.net/p/cxx/code/trunk/CXX>

> 
> >>> c = simple.OldClass()
> >>> a = b + c
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: unsupported operand type(s) for +: 'simple.OldClass' and 'simple.OldClass'

You have to implement the number_add method. See Demo/Python3/simple.cxx 
 
> 
> 
> My purpose is to expose and use in Python my C++ class as a new type. I need support for different constructors, like:
> 
> >>> a = simple..OldClass("a")
> >>> a = simple..OldClass(5)
> 
No problem look at simple.cxx and the c'tor for new_style_class.

    new_style_class( Py::PythonClassInstance *self, Py::Tuple &args, Py::Dict &kwds )

You can handle args and kwds as you need to implement your API.

> 
> I hope my questions are not too confusing 

Barry