autoborg &c (was )e:d Unified Type/class (Singleton)

[Pedro Rodriguez]

"Pedro Rodriguez" <pedro_rodriguez at club-internet.fr> wrote:

> "Alex Martelli" <aleax at aleax.it> wrote:
> 
>> "Pedro Rodriguez" <pedro_rodriguez at club-internet.fr> wrote in message
> 
>>> Ok. Except for a probable typo on 'C.__call__' which may exist or not
>>> but is not involved in this process (your examples suggests
>>> C.__new__).
>> 
>> Wrong, at least in the simplest case:
>> 
>>>>> class C(object): pass
>> ...
>>>>> C.__call__
>> <method-wrapper object at 0x007B4200>
>>>>> y=C.__call__()
>>>>> y
>> <__main__.C object at 0x007B6FB0>
>> 
>> C.__call__ does indeed exist (and here comes from C's type, i.e. the
>> type metaclass), and is exactly what's involved when you call C
>> ("typically comes from C.__class__", as I said).
>> 
>> Of course, if C's class-body defines an attribute or method __call__:
>> 
>>>>> class C(object):
>> ...   def __call__(self): print '!'
>> ...
>>>>> C.__call__
>> <unbound method C.__call__>
>> 
>> then C.__call__ comes to mean something else, because of how
>> object.__getattr__ is coded.  C.__class__.__call__ (if any) is
>> typically what's involved in calling C.
>> 
>> 
> This could be confusing, but I am sure there is a reason in Python
> internals.
> 
> I understand that a __call__ defined in a class turned its instances
> into callables. So why should a class have a __call__ attribute with a
> different semantic by default (C.__call__() == C() ?)
> 
> It seems to come from the 'type' object and slot allocation in
> typeobject.c :
>    >>>> help(type) returns :
>    ...
>    __call__(...)
>       x.__call__(...) <==> x(...)
>    ...
> 
> The best explanation I can think of is : all slots (for future '__xxx__'
> attributes) need to be allocated for class objects. They get a semantic
> and this is a default value.
> 
> Notice that, when not defined by the developer, it doesn't appear with
> dir() ( from descrintro : 'It does not show class attributes that are
> defined by a metaclass', I think if falls in this category).
> 
> 

Forget about my crap. There are simpler explanations but it will take
me some time to formulate them properly.
Must not be the first one being stroke by metaclasses ;)

Sorry...
-- 

Pedro