"my brain hurts" or is isinstance broken?

[Jonathan Hogg]

On 3/7/2002 14:55, in article
eaef2e43.0207030555.1a63fe10 at posting.google.com, "Robert Kuzelj"
<robert_kuzelj at yahoo.com> wrote:

> one could imagine an object that is a mix between a factory and
> a prototyperegistry.
> 
> class ProtoFactory:
>  def __init__(self):
>     self.SourceObjects = {}
>  def register(self, name, source):
>     self.SourceObjects[name] = source
>  def create(self, name):
>     source = self.SourceObjects(name)
>     if isinstance(source, types.Instance.Type):
>        return copy.copy(source)
>     else:
>        return source()

Hmmm. Well I can think of a couple of possibilities:

1. Reverse the test and check to see if something is an instance of 'type'
   of 'types.ClassType', i.e., a new-style class or an old-style class.

   if isinstance(source, type) or isinstance(source, types.ClassType)
       return source()
   else:
       return copy.copy( source )

2. If you know that the instances you are creating will not have '__call__'
   methods, then you can differentiate classes and instances by the fact
   that classes are callable:

   if callable( source ):
       return source()
   else:
       return copy.copy( source )

   This works equally well for old- and new-style classes. Conveniently it
   also works functions that create objects and callable instances
   masquerading as classes or functions that create objects (hoo hah).

> this is just an example. i am sure, that this can be done
> differently. the real reason why i want to do this is something
> i realy dare not to say in this forum ;-)

Oh, you can tell us. No matter what crimes your contemplating, you can take
comfort in the fact that they can probably be made more horrifying with
metaclasses ;-)

Jonathan