RE: Embedding Python

[carlos c. <hap...@ho...>]

Thanks for the prompt reply.

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?

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"?

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

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

 >From: Barry Scott <ba...@ba...>
 >Reply-To: Discuss PyCXX use and improvement
 ><cxx...@li...>
 >To: Discuss PyCXX use and improvement <cxx...@li...>
 >Subject: Re: Embedding Python
 >Date: Sun, 3 Dec 2006 19:33:04 +0000
 >
 >
 >On Dec 1, 2006, at 18:54, carlos choy wrote:
 >
  I am thinking of using PyCXX principally for embedding Python.
 >
 >This works. You will need to create a module using PyCXX if you
 >wish the python code to be able to call you back.
 >
 >If you use threads there is extra work in the init and in the module
 >you will need to worry about.
 >
 >
  Here is some
  basic code for embedding that I intend to use:

  ****************************************************************
  #include <Python.h>

  int main(int argc, char *argv[])
  {
      PyObject *pName, *pModule, *pDict, *pFunc, *pValue;

 >
 >Use appropriate Py:: objects.
 >
      if (argc < 3)
      {
          printf("Usage: exe_name python_source function_name\n");
          return 1;
      }

 >
 >	Give python an argc and argv before calling init.
 >
      // Initialize the Python Interpreter
      Py_Initialize();

      // Build the name object
      pName = PyString_FromString(argv[1]);
 >
 >	Py::String name( argv[1] );
 >

      // Load the module object
      pModule = PyImport_Import(pName);
 >
 >	Py::Module module( PyImport_Import( name ) );
 >
      // pDict is a borrowed reference
      pDict = PyModule_GetDict(pModule);
 >
 >Py::Dict dict( module.getDict() );
 >

      // pFunc is also a borrowed reference
      pFunc = PyDict_GetItemString(pDict, argv[2]);
 >
 >	Py::Callable func( dict[ Py::String( argv[2] ) ] );
 >

      if (PyCallable_Check(pFunc))
      {
          PyObject_CallObject(pFunc, NULL);
      } else
      {
          PyErr_Print();
      }
 >
 >No need to do the if an exception will be raise if an objects type
 >does not match.
 >
 >	// no args
 >	Py::Tuple args( 0 );
 >
 >	func.apply( args );
 >
      // Clean up
      Py_DECREF(pModule);
      Py_DECREF(pName);
 >
 >	No need to call dec.
 >	But you will need to make sure that the Py:: onjects go out of scope
 >so that
 >	they are deleted before calling finalize.
 >

      // Finish the Python Interpreter
      Py_Finalize();

      return 0;
  }
  **********************

  I assume the above will work.  Is there a more PyCXX way of doing
  this?
 >
 >See comments in line above.
 >

  Lastly, I need to have callbacks into C++ code from Python.  The
  Callable
  interface is documented, but samples.  Can someone please post
  examples of
  how to use it?

  _________________________________________________________________
 >
 >Define a module and add functions and classes. Look at the example
 >that comes with PyCXX in the Demo folder. For example look at
 >range.hxx and .cxx.
 >
 >If you want a full scale example look at the source of the Python SVN
 >extension, pysvn
 >at http://pysvn.tigris.org - download a source kit add you will see
 >examples of calling C++ from
 >python and calling python from C++.
 >
 >Barry
 >
 >
 >
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