PyCXX Python-C++ Connection

On 9 Apr 2010, at 15:27, Fernando Libonati wrote:

> Two questions ...
> a) How can I pass a pointer to a new type object?

Can you get a pointer from a Py::Object? Yes

> b) Can I access methods from this pointer?

yes. But it depends on the method. If its
a C++ method then its trivia. If its a python method
on the object that may have been overridden in
a derived class then you need to use a PyCXX helper.

The code below depends on PyCXX trunk that I will release
as 6.2.0 soon.


> 
> Like in
> 
> class Block : Public PythonClass<Block> {
>      Block *parent;
>      Block(Py::PythonClassInstance *self, Py::Tuple &args, Py::Dict &kwds):
>      : Py::PythonClass< Block >::PythonClass( self, args, kwds )
>     {
>         args.verify_length(1);
>        // Is this possible ??? or something like this
>         parent  = (Block*) args[0]; 

This does not work on lots of levels.
a) Py::Object just holds a pointer to the PyObject.
b) You cannot cast a PyObject as its not part of the C++ class.
     It contains a pointer to the C++ class.

Use this to make sure you really have a Block:

	Py::PythonClassObject<Block> py_block( args[0] );

Now you can get the C++ object pointer:

	Block *p_block = py_block.getCxxObject();

To call getFullName you have a couple of choices:

	Py::String s( p_block->getFullName() );

or

	Py::TupleN args;
	Py::String py_block.callMemberFunction( "getFullName", args );


>     }
> ...
> ...
>     Py::Object getFullName( void )
>     {
>         std::string r = "";
>         if( ! parent->isNone() )
>             r += Py::String( parent->getFullName()).as_std_string( "utf-8" ) + ".";
> 
> /* I want to access parent's methods directly to avoid the overload of calling
>    callMemberFunction("getFullName") and many others that I need.
>    Is it possible? 
>    Is callMemberFunction restricted to the exposed ones?
> */
>         r += name.as_std_string( "utf-8" );
>         return Py::String(r);
>     }
> ...
> ...
> };
> 

Barry

Excellent explanation !

I promise to start a deeper study of the code this weekend in order to
minimize bothering you (but not stop, ha ha).

Fernando

2010/4/9 Barry Scott <barry@...>

>
> On 9 Apr 2010, at 15:27, Fernando Libonati wrote:
>
> Two questions ...
> a) How can I pass a pointer to a new type object?
>
>
> Can you get a pointer from a Py::Object? Yes
>
> b) Can I access methods from this pointer?
>
>
> yes. But it depends on the method. If its
> a C++ method then its trivia. If its a python method
> on the object that may have been overridden in
> a derived class then you need to use a PyCXX helper.
>
> The code below depends on PyCXX trunk that I will release
> as 6.2.0 soon.
>
>
>
> Like in
>
> class Block : Public PythonClass<Block> {
>      Block *parent;
>      Block(Py::PythonClassInstance *self, Py::Tuple &args, Py::Dict &kwds):
>      : Py::PythonClass< Block >::PythonClass( self, args, kwds )
>     {
>         args.verify_length(1);
>        // Is this possible ??? or something like this
>         parent  = (Block*) args[0];
>
>
> This does not work on lots of levels.
> a) Py::Object just holds a pointer to the PyObject.
> b) You cannot cast a PyObject as its not part of the C++ class.
>      It contains a pointer to the C++ class.
>
> Use this to make sure you really have a Block:
>
> Py::PythonClassObject<Block> py_block( args[0] );
>
> Now you can get the C++ object pointer:
>
> Block *p_block = py_block.getCxxObject();
>
> To call getFullName you have a couple of choices:
>
> Py::String s( p_block->getFullName() );
>
> or
>
> Py::TupleN args;
> Py::String py_block.callMemberFunction( "getFullName", args );
>
>
>     }
> ...
> ...
>     Py::Object getFullName( void )
>     {
>         std::string r = "";
>         if( ! parent->isNone() )
>             r += Py::String( parent->getFullName()).as_std_string( "utf-8"
> ) + ".";
>
> /* I want to access parent's methods directly to avoid the overload of
> calling
>    callMemberFunction("getFullName") and many others that I need.
>    Is it possible?
>    Is callMemberFunction restricted to the exposed ones?
> */
>         r += name.as_std_string( "utf-8" );
>         return Py::String(r);
>     }
> ...
> ...
> };
>
>
> Barry
>
>
>
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-- 
Fernando Libonati
fernando.libonati at gmail.com