Simple questions on use of objects (probably faq)

[bruno at modulix]

Brian Elmegaard wrote:
> bruno at modulix <onurb at xiludom.gro> writes:
> 
> 
>>Now how you could do it the OO way (Q&D, not really tested):
> 
> 
> Something goes wrong in my 2.3 

So it's time to move to 2.4x !-)

What is "going wrong" exactly ?

> when I change the syntax to
> _add_instance=classmethod(_add_instance).

> If I understand this correctly the class is keeping track of the
> instances of itself.

Yeps.

> The class is extendible and has all the needed
> methods. This means that any global lists can be
> avoided. 

Yeps too. This is called "encapsulation".

But this also means you only have one list of instances - which may or
may not be ok for what you're trying to do. Note that there are possible
workarounds, like using a dict of lists:

class Foo(object):
  _instance_lists = {}

  def __init__(self, x, list_id):
    self.x = x # no, you won't avoid it
    self._add_instance(self, list_id)

  @classmethod
  def _add_instance(cls, instance, list_id):
     cls._instance_lists.setdefault(list_id, []).append(instance)

  @classmethod
  def get_instances(cls, list_id):
    return cls._instance_lists[list_id].[:]

  # now you need to add the list_id parameter to all others classmethods

Also, if you intend to use such a solution (with or without multiple
lists), you may want to add a classmethod to delete instances from the
list(s).



-- 
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb at xiludom.gro'.split('@')])"