Two way communication between a python class and a C++ class

[Dave Kuhlman]

What you are looking for (if I understand you) is a way to pass an
instance of a C++ class to Python so that the Python code can call
a method in that class.

Stop me if I'm wrong about that ...

But, if I'm right, then consider doing the following:

Implement a new Python data type.  Implement it in C/C++. An
instance of this data type will hold (internally) a pointer to the
instance of your C++ class, and it will "expose" to Python one or
more methods, which will call the methods in (the instance of) your
C++ class.

Think about the list built-in class in Python.  It wraps a C list
object, and when you do:

    mylist = []
    mylist.append('hello')

It calls an append function (implemented in C) for that object.

How to implement it -- Get the Python source distribution.  Look in
the Objects subdirectory for a file Objects/xxobject.c.  Copy and
rename that file.  Then follow the suggestions in the comments at
the top of that file.

Also look for help in:

    http://www.python.org/doc/current/ext/defining-new-types.html

I've also written a tool to help generate the source code for
simple cases where little more than a wrapper for a C struct is
needed.  It's called dtGenerator.py and you can find out about it
at:

    http://www.rexx.com/~dkuhlman/

Hope this helps.  And, let us know if/when you have more questions.

  - Dave


Firestar <dwjoker at thenorth.org> wrote:
> 
> Hi,
> 
> I am having a problem obtaining two way communication between a python
> class and a c++ class. I can get a python class to communcate with a
> c++ class and a c++ class to communicate with a python class, but i
> cannot seem to get the communication to go both ways.
> 
> i.e I have a class CTest in c++ and a class PTest in python and when i
> create an instance of CTest in c++ it creates an instance of PTest in
> python, i then want PTest to be able to call methods in the instance
> of CTest that created the instance of PTest. How can i do this? there
> seems to be no way to pass the c++ pointer into the python class in
> the constructor...
> 
> There must be a way... does anyone know how to do this??? Help much
> appreciated!!
> 
> Firestar

-- 
Dave Kuhlman
dkuhlman at rexx.com


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