Re: [Swig-user] Pass PyObject*'s through SWIG interface

[James B. <bi...@cs...>]

James Bigler wrote:
> I'm trying to make some python callbacks from C.  So far I wrote a 
> simple interface by hand (not using swig) that allows me to pass a 
> function and its arguments from python to C.  I create an class object 
> (called MyPyCallback) with PyObject pointers to the function and args 
> and pass that back in a PyCObject. This can then be stored in python or 
> in C and used to call the function later.
> 
> Now I have an interface generated by swig that provides all sorts of 
> access to callback mechanisms.  I need a way to pass this PyCObject 
> through the interface to make it into something I can pass around.
> 
> My question is how I can pass the PyObejct*'s directly through the 
> interface. If need be I can make a wrapper for MyPyCallback, in which 
> case all I need is a way to get the void* in the PyCObject into a 
> Swigged MyPyCallback*.
> 
> Any pointers to where I should look in the documentation or other help 
> would be appreciated.

After reading pages and pages of the documentation, I discovered I could do this 
through %typemap.  Here is some simple code that counts the number of items in a 
tuple passed in:

%typemap(in) PyObject* {
   $1 = $input;
}

// This is for other functions that want to return a PyObject.
%typemap(out) PyObject* {
   $result = $1;
}

int countTuple(PyObject* args);

%{
   int countTuple(PyObject* args) {
     if (!PyTuple_Check(args)) {
       fprintf(stderr, "Not a Tuple\n");
       return 0;
     }
     int num_args = PyTuple_Size(args);
     return num_args;
   }
%}

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

I don't care that this isn't language portable, since I just want to use python. 
  I now have a class that stores pointers to python functions and their 
arguments, that I can call later from C.

Thanks,
James