[Python-3000] Method descriptors

[Guido van Rossum]

On Dec 10, 2007 2:57 PM, Marcin 'Qrczak' Kowalczyk <qrczak at knm.org.pl> wrote:
> Dnia 10-12-2007, Pn o godzinie 11:01 -0800, Guido van Rossum pisze:
>
> > Add a __get__ (instance) method to f's class, and store f directly in
> > A. Your __get__ method should return a bound object using
> > PyMethod_New(f, a).
>
> Thank you, but I can't do this, because I want a generic mechanism which
> works for an arbitrary f (which will probably be a Kogut object wrapped
> in Python, and not all such objects play the role of methods but they
> use the same type).
>
> I solved this by a separate Python type, which is a simple wrapper not
> specific to my other types, so I'm a bit surprised that there is no
> such type among various wrappers and descriptors in the Python core
> (or perhaps I overlooked it somewhere). It wraps a single object f, and
> its get_descr(m, obj, type) returns PyMethod_New(f, obj) (for Python3)
> or PyMethod_New(f, obj, type) (for Python2), except that if obj == NULL,
> it returns f itself.
>
> It's even better than PyMethod_New(f, NULL, type) in that it does not
> need to know the class when created.

I guess there's no such egneric wrapper in the core because the use
case hasn't presented itself before -- or nobody thought of creating a
generic solution.

It's also possible that in the past this was done using unbound
methods -- so perhaps their removal from the method object may have
been premature.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)