Callback mysteries

[Fons Adriaensen]

Hello all,

I wonder if someone could explain some of the following.

(Python 3.2)

I have a class which has a method called 'callback()'.
An instance of this class calls a C extension which
then calls back into Python.

In all cases below, two arguments are passed to the C
code and end up in 

PyObject *object;
PyObject *method;

The original solution was:

P:  self -> object,  "callback" -> method
C:  PyObject_CallMethodObjArgs(object, method, 0);

and this works nicely. 

Just out of academic interest, I was wondering if the run-time
lookup of 'callback' could be avoided. My first attempt was:

P:  self -> object, classname.callback -> method
C:  PyObject_CallFunctionObjArgs(method, object, 0); 

and this also works, I'm just not sure it's kosher.

Now in theory 'self.callback' should contain all info
that is required (or not ?). So I also tried:

P:  self -> object, self.callback -> method
C:  PyObject_CallFunctionObjArgs(method, PyMethod_Self(method), 0)

which fails,  

P:  self -> object, self.callback -> method
C:  PyObject_CallFunctionObjArgs(PyMethod_Function(method), PyMethod_Self(method), 0);

which also fails.

And indeed the value returned by PyMethod_Self() is not equal to 
the value of object (= self). In fact it seems not to depend on
the calling instance at all. Do I misunderstand what PyMethod_Self()
is supposed to return ?

I also tried 

P:  self -> object, self.callback -> method
C:  PyObject_CallObject(method, 0);

which also fails.

Any comments that help me understand these things will be appreciated !


Ciao,

-- 
FA