It is possible to pass a Python callback to C-extensions?

[Gerhard Häring]

Sure. Explanation by example:

Python code:

#v+
def myfunc(): pass

foobar.register_callback(myfunc)
#v-

C code:

#v+
PyObject* register_callback(FooType* self, PyObject* args, PyObject** 
kwargs)
{
	/* ParseTupleAndKeywords */
	/* PyCallable_Check */
	self->callback = ...
}

...
	function_result = PyObject_CallObject(callback, calling_args);
...
#v-

No idea about SWIG, but I do this a lot in the PySQLite code using 
Python's raw C API, which you could use as an example:

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/pysqlite/pysqlite/_sqlite.c?rev=HEAD&content-type=text/vnd.viewcvs-markup

HTH,

-- Gerhard