[Python-3000] Method descriptors

[Marcin ‘Qrczak’ Kowalczyk]

I'm confused about storing methods in class dictionaries from the point
of view of the C API.

1. Let's say that I have a callable PyObject called f, of my type
   defined in C. I want to store something derived from f as A.m
   for some class A, such that for an object a of class A, calling
   a.m(*args) ends up calling f(a, *args).

   In Python2 PyMethod_New(f, NULL, a) seems to be the right to store
   in the class. How to do the equivalent thing in Python3?

   BTW, applying PyMethod_Type to 3 arguments crashes Python3. I think
   this line is the culprit (classobject.c):

        if (!PyArg_UnpackTuple(args, "method", 2, 3,
                              &func, &self))

   Should be 2 instead of 3. There used to be an extra parameter.

2. As above, but f is to be implemented as a C function. I found the
   following working for a new-style class:

   - make PyMethodDef struct for the method
   - use PyDescr_NewMethod
   - store the resulting object in the class

   but it does not work for a classic class (such that an exception
   class in Python 2.4 and below) to which I want to add a method.
   Here it seems to be doable differently:

   - make PyMethodDef struct for the method, but with an unused first
     parameter
   - use PyCFunction_New, with NULL as 'self'
   - use PyMethod_New on the resulting function, NULL, and the class
   - store the resulting object in the class

   Can this be done simpler? Having separate variants for different
   Python versions is OK.

-- 
   __("<         Marcin Kowalczyk
   \__/       qrczak at knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/