Re: Embedding Python

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

On Dec 8, 2006, at 17:07, carlos choy wrote:

> I looked at the Demo folder and found usage of the Callable  
> interface in
> rangetext.cxx.
> In version 5.36, rangetest.cxx has the following lines (starting at  
> line
> 29):
>
> *******************************************
>     RangeSequence r2(1, 10, 2);
>     if(r2[1] != Py::Int(3))
>         return "RangeSequence check failed. ";
>
>     debug_check_ref_queue();
>
>     // calling an extension object method using getattr
>     Py::Callable w(r2.getAttr("amethod"));
>     Py::Tuple args(1);
>     Py::Int j(3);
>     args[0]=j;
>     Py::List answer(w.apply(args));
>     if(answer[0] != r2)
>         return ("Extension object test failed (1)");
>
>     if(answer[1] != args[0])
>         return ("Extension object test failed (2)");
> *******************************************
>
> I see that RangeSequence is a class extending a python sequence.   
> However, I
> don't see how "amethod" could be an attribute of it.  "amethod" is  
> a method
> of the range class, but this class seems to have nothing to do with
> RangeSequence.  How is this method an attribute of the extended class?


RangeSequence is Py::Object that points to an instance of range. See  
line 112 of range.hxx.


> Next, I see that 'w' is a Callable object, but I do not see how it  
> can have
> an 'apply' method.  Is the 'apply' method putting the arguments in  
> 'args'
> into the method "amethod"?

It works the same way that apply builtin works in python. Call the  
function that w contains
passing it args and store the returned value in answer.

>
> Lastly, I don't see at all how the Callable object is calling back  
> into a
> python script.

The apply() functions calls into python.

>
> Can you please give me some explanations?  Sorry if this all seems  
> rather
> elementary, but I am trying my best to understand it.


No problem.


Barry