[C++-sig] How to use own C++/python bindings in embeddedinterpreter.

[Pierre Bourgault]

Hi Roman, 

Thanks for your reply. I know how to expose C++ classes to Python. The
problem I have is that the class registration is done in
init_module_whatever() (BOOST_PYTHON_MODULE) and I want to a python
instance of an object of this class in C++ and giving it to a script,
without having to duplicate the code. 

I found a solution (which is to obtain the class object from my module's
dictionary) and I thought I should share it. At the same time, if a
better way exists, I am sure someone will point it out (I suppose that I
could also replace most of the Python/C API calls by boost::python
calls). 

In myClass.hpp, I have the following C++ class:
-----------------------------------------------
class MyClass {
public:
    MyClass();
    void doit()
}

In whateverInit.cpp I have:
---------------------------
BOOST_PYTHON_MODULE(whatever)
{
  class_<MyClass>("MyClass").def( "doit", MyClass::doit);
}

That allows me to have a python script that does this:
------------------------------------------------------
# useMyClass.py
import whatever
a = new MyClass()
a.doit()

==================================================================

Now I want to call func() defined in scriptWithFunc.py from C++, 
passing it a python instance of MyClass, but created first in C++:
# scriptWithFunc.py
import whatever
def func(myobj):
   myobj.doit()

SOLUTION: The C++ code that calls func():
-----------------------------------------

// callScriptFunc.cpp
// 
str script = "scriptWithFunc";
str function = "func";
object moduleWithFunc = PyImport_Import(script);
object func = PyObject_GetAttrSring( moduleWithFunc, function );
if (!(func && PyCallable_Check(func))) { 
   return;
}

// import module "whatever"
handle<> module(PyImport_Import("whatever")); 
object theModule(handle<>(borrowed(PyImport_AddModule("whatever"))));
// Obtain its dictionary and get the object representing class MyClass.
dict d = extract<dict>(dict(theModule.attr("__dict__"));
object MyClass_Class = d[ 'MyClass' ]

// Create an instance
myObj = MyClass_Class()

PyTuple_SetItem(args, myObj.ptr());
PyObject_CallObject(function, args);


-----Original Message-----
From: Roman Yakovenko [mailto:roman.yakovenko at gmail.com] 
Sent: January 17, 2007 9:43 AM
To: Development of Python/C++ integration
Subject: Re: [C++-sig] How to use own C++/python bindings in
embeddedinterpreter.

On 1/17/07, Pierre Bourgault <pierre.bourgault at autodesk.com> wrote:
> I have the following C++ class defined in myClass.h in my application:

Google is your friend :-). Py++ site (
http://www.language-binding.net/ ) uses Google Custom Search engine,
which is configured to provide better results for Boost.Python related
searches.

Second result for "construct python object" search string brings next
link http://wiki.python.org/moin/boost.python/class

BOOST_PYTHON_MODULE(example1)
{
  object class_a = class_<A>("A");

  object instance_a = class_a();
}

-- 
Roman Yakovenko
C++ Python language binding
http://www.language-binding.net/