Special Method and Class

[Yermat]

Jack Diederich wrote:
> On Thu, Apr 08, 2004 at 02:47:49PM -0400, Jack Diederich wrote:
> 
>>On Thu, Apr 08, 2004 at 08:07:01PM +0200, Yermat wrote:
>>
>>>Hi all,
>>>
>>>Why does special methods not work on class ? Or how to make them work ?
>>>Here a simple example :
>>>
>>>
>>>>>>class Test(object):
>>>
>>>...     def __repr__(cls):
>>>...         return "<special %s>" % cls.__name__
>>>...     __repr__ = classmethod(__repr__)
>>>...
>>>
>>>>>>print repr(Test)
>>>
>>><class '__main__.Test'>
>
>This is your clue, this didn't print <special Test>
>for the same reason the __iter__ does work below.
>The special __method__'s only work for instances of
>the class and not for the class itself.
>
>>
>>>>>print repr(Test)
>>
>><class '__main__.Test'>
>>
>>>>>print repr(Test())
>>
>><special Test>
> 
> 
> This deserves a better explanation,
> repr(some_instance) will call the __repr__ method of the thing that foo
> is an instance of. 
> 
> You normally think of objects as instances of a class, but classes are 
> also an instances of a type.  Now you're in metaclass territory which 
> is overkill for what you want to do.
> 
> illustration:
> 
> class MetaFoo(type):
>   """define our own type"""
>   def __repr__(self):
>     return 'this is an instance of MetaFoo'
> 
> class Foo(object):
>   """define a class which is an instance of our own type"""
>   __metaclass__ = MetaFoo
>   def __repr__(self):
>     return 'this is an instance of Foo'
> 
> 
>>>>repr(Foo)
> 
> 'this is an instance of MetaFoo'
> 
>>>>repr(Foo())
> 
> 'this is an instance of Foo'
> 
> I can't think of a reason that classmethod() would be useful or legal
> when applied to magic methods like __repr__.  Maybe it should throw
> an exception instead.  It is possible to do things with a classmethod
> __repr__ but it is a very obscure way to get the end effect.
> 
> def Foo(object):
>   which = 'class'
>   def __init__(self):
>     self.which = 'instance'
>   def __repr__(cls):
>     return "Foo with which of " + cls.which
>   __repr__ = classmethod(__repr__)
> 
> 
>>>>repr(Foo())
> 
> 'Foo with which of class'
> 
> 
> -jackdied
> 


Ok thanks, I see my mistake !
I thought that those special method were bounded methods but they are not...

 >>> class toto(object):
...     def __init__(self, name):
...             self.name = name
...     def __repr__(self):
...             return "toto('%s')" % self.name
...
 >>>
 >>> t = toto('titi')
 >>> repr(t)
"toto('titi')"
 >>> t.__repr__
<function anotherRepr at 0x402dc454>
 >>> t.__init__
<bound method toto.__init__ of toto('titi')>

That also mean that I can't change the __repr__ for only one instance :
 >>> def anotherRepr(self):
...     return "anotherRepr('%s')" % self.name
...
 >>>
 >>> t.__repr__ = anotherRepr
 >>>
 >>> repr(t)
"toto('titi')"


Is it really consistent ?
Should'nt it be also bounded methods even for clas instead of using 
MetaClass ?

Yermat