overriding method that returns base class object

[Aahz]

In article <40315037$0$199$75868355 at news.frii.net>,
Stuart McGraw <smcg4191 at frii.RemoveThisToReply.com> wrote:
>
>Class A has a method A.a() that returns an A.  I want a 
>identical class but with an additional property .newprop
>and method .b()  And I want .a() to return a B, not an A.
>
>  class B (A):
>    def __init__(self, *args, **kwds):
>      A.__init__(self, *args, **kwds)
>      self.newprop = 99
>    def a(self):
>      x = A.a(self)    # x is an A
>      x.__class__ = B
>      return x    # I want x to be a B, i.e have b() and .newprop.
>    def b(self):
>      ...something...
>
>Yes, I know this is bogus.  But I am not sure what I should be doing.
>And to correct what I originally posted, A is implented in python
>(but I still can't change it for administrative reasons), but it's
>properties are declared with "__slots__ = [...]" if that makes a
>difference.  This is all in Python 2.3.3.

class A:
    def a(self):
        return self.__class__()
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

"Argue for your limitations, and sure enough they're yours."  --Richard Bach