How User-defined method objects are created?

Joaquin Abian gatoygata2 at gmail.com
Sat Mar 20 22:32:40 CET 2010


On Mar 20, 5:39 pm, Terry Reedy <tjre... at udel.edu> wrote:
> On 3/20/2010 9:54 AM, Joaquin Abian wrote:
>
>
>
> > I'm trying to understand the description of method object creation in
> > the python 2.6 language reference (3.2. The standard type hierarchy)
> > with little success. The points knocking me are:
>
> > "User-defined method objects may be created when getting an attribute
> > of a class (perhaps via an instance of that class), if that attribute
> > is a user-defined function object, an unbound user-defined method
> > object, or a class method object. When the attribute is a user-defined
> > method object, a new method object is only created if the class from
> > which it is being retrieved is the same as, or a derived class of, the
> > class stored in the original method object; otherwise, the original
> > method object is used as it is."
>
> > It is a bit of a tongue-twister for me. What the last sentence means?
> > Please, I beg for a simple example of the different objects (user
> > defined function, user defined method, class method) refered.
> > Are maybe the refered objects exemplified by :
>
> > #python 3.1
> > class Klass():
>
> >    def met(self):
> >            print('method')
>
> >         def func():
> >            print('function')
>
> >         @classmethod
> >    def kmet(klass):
> >            print('classmethod')
>
> > or it is talking about another thing?
> > What is the difference with python 3 where there is no mention to the
> > unbound user-defined method object (same section in python 3 language
> > reference):
>
> Python3 does not have unbound method objects. Klass.met above is just a
> function.l
>
> > "User-defined method objects may be created when getting an attribute
> > of a class (perhaps via an instance of that class), if that attribute
> > is a user-defined function object or a class method object."
>
> > I'm trying to learn, however the task is revealing as an enormous
> > undertaking :-)
>
> One can successfully use the language in the normal way without
> understanding every detail of every oddball corner case. Recent 2.x is
> complicated by duplication (two user object systems) and
> back-compatibility constraints. Most new users do not need to bother
> with obsolete complications.
>
> Terry Jan Reedy

Terry, Right, I was just reading about this difference in 2 vs 3 in
Lutz's book.
Well, in fact in my case I'm not a newcomer to python (neither a
professional). I have been programming for more than 4 years in python
mainly medium size scientific data management applications. Currently
I can write at a moderate speed and Im familiar with properties,
decorators, etc.

That's why it is so frustrating went I get lost in the language
reference manual in a matter I wrongly though was a simple stuff.

Thanks for your helpful comments.

JA



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