super, decorators and gettattribute

[Michele Simionato]

Re: super, decorators and gettattribute

On Jan 14, 11:47 pm, Richard Szopa <ryszard.sz...@ gmail.comwrote:

Could you tell me what are the pros and cons of the two approaches
(i.e. writing a decorator function and a decorator descriptor class)?

I prefer to use a class for introspection sake, since
there is no way to get information about an inner function
in a closure, whereas your users can introspect classes
pretty well.

super_object = super(self.__cl ass__, self)

Notice that using super(self.__cl ass__, self) is a common
mistake: the pitfalls with inheritance were discussed
very recently in this same newsgroup, you should be
able to find the post. What you need is

super(class_whe re_the_method_i s_defined, self)

which is in general different from

super(self.__cl ass__, self)

There is no clean way to determine the current class
in Python < 3.0 (Python 3.0 does it automatically);
if you want to see a hackish way involving
bytecode tricks see

http://groups.google.com/group/comp.lang.python/browse_frm/thread/a6010c7494871bb1/62a2da68961caeb6?hl=en&lnk=gst&q=currentClass#62a2da68961caeb6

(and notice that this is really not recommended).

Michele Simionato

[Rhamphoryncus]

Re: super, decorators and gettattribute

On Jan 13, 5:51 am, Richard Szopa <ryszard.sz...@ gmail.comwrote:

On Jan 13, 8:59 am, Marc 'BlackJack' Rintsch <bj_...@gmx.net wrote:
>

On Sat, 12 Jan 2008 14:23:52 -0800, Richard Szopa wrote:

However, I am very surprised to learn that

>

super_object.__ getattr__(name) (*args, **kwargs)

>

getattr(super_o bject, name)(*args, **kwargs)

>

are not equivalent. This is quite odd, at least when with len()
and .__len__, str() and .__str__. Do you maybe know what's the
rationale behind not following that convention by getattr?

>

I think you are confusing `__getattr__` and `__getattribute __` here!
`getattr()` maps to `__getattr__()` , it's `__getattribute __` that's
different.

>
Well, in my code calling super_object.__ getattr__(name) (*args,
**kwargs) and getattr(super_o bject, name)(*args, **kwargs) gives
*different* effects (namely, the latter works, while the former
doesn't). That kinda suggests that they don't map to each other :-).
And that makes me feel confused.

Don't think of them as mappings. Think of them as a way for a class
to hook into getattr's protocol, conveniently named similar to getattr
(__getattr__ and __getattribute_ _). getattr() may call several
methods, no methods at all, change the arguments, etc. Although len()
may seem simple, many others are not so simple.

--
Adam Olsen, aka Rhamphoryncus

[Helmut Jarausch]

Re: super, decorators and gettattribute

Michele Simionato wrote:

I really need to publish this one day or another, since these
questions
about super keeps coming out:
>
http://www.phyast.pitt.edu/~micheles/python/super.html

Unfortunately the links [2], [3] and [4] are not given,

Helmut.


--
Helmut Jarausch

Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany

[Richard Szopa]

Re: super, decorators and gettattribute

On Jan 15, 8:06 pm, Helmut Jarausch <jarau...@skyne t.bewrote:

Unfortunately the links [2], [3] and [4] are not given,

Luckily, there's Google :)

[2] Article about MRO: http://www.python.org/download/releases/2.3/mro/
[3] Descriptor HowTo: http://users.rcn.com/python/download/Descriptor.htm
[4] Articles about metaclasses (second one relevant to super):
* http://www.ibm.com/developerworks/li.../l-pymeta.html,
* http://www-128.ibm.com/developerwork...GX03&S_CMP=ART,
* http://www.ibm.com/developerworks/li...GX03&S_CMP=ART

Of course, it would be very nice if the article was updated to include
the links.

HTH,

-- Richard