[Python-Dev] Meta-reflections

[Kevin Jacobs]

On Wed, 20 Feb 2002, Gordon McMillan wrote:
> On 20 Feb 2002 at 8:30, Kevin Jacobs wrote:
> > Attributes currently have a flat namespace,
>
> Instance attributes do, but that's a tautology.

Yes, though one implication of the new slots mechanism in Python 2.2 is that
we now have have non-flat per-instance namespaces for slots.  i.e., we would
have per-instance slots that would hide other per-instance slots of the same
name from ancestor classes:

  class Base(object):
     __slots__ = ['foo']
     def __init__(self):
       self.foo = 1          # which slot this sets depends on type(self)
                             # if type(self) == Base, then the slot is
                             # described by Base.foo.
                             # else if type(self) == Derived, then the
                             # slot is described by Derived.foo

   class Derived(Base):
     __slots__ = ['foo']
     def __init__(self):
       Base.__init__(self)
       self.foo = 2          # this is NOT the same foo as in Base

  o = Derived()
  print o.foo
  > 2
  o.__class__.__base__.foo = 3
  print o.foo
  > 2
  print o.__class__.__base__.foo
  > 3

So slots, as currently implemented, do not act like attributes, and this
whole discussion revolves around whether they should or should not.

Regards,
-Kevin

--
Kevin Jacobs
The OPAL Group - Enterprise Systems Architect
Voice: (216) 986-0710 x 19         E-mail: jacobs@theopalgroup.com
Fax:   (216) 986-0714              WWW:    http://www.theopalgroup.com