Special Method and Class

[Jack Diederich]

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>

> import weakref
> class RememberInstance(object):
>     instances = []
> 
>     def __init__(self,name):
>         self.name = name
>         self.__class__.instances.append(weakref.ref(self))
> 
>     def __iter__(cls):
>         for wref in cls.instances:
>             inst = wref()
>             if inst:
>                 yield inst
>     __iter__ = classmethod(__iter__)
> 
> 
> t1 = RememberInstance('t1')
> t2 = RememberInstance('t2')
> 
> for inst in RememberInstance:
>     print inst.name
> 

drop the __iter__ altogether and just iterate over the class's list

for (inst) in RememberInstance.instances:
  if (inst()): # the weakref hasn't expired
    print inst().name

It is much clearer and less magic to boot.

-jackdied