Type casting a base class to a derived one?

[Frederic Rentsch]

Hi all,
   If I derive a class from another one because I need a few extra 
features, is there a way to promote the base class to the derived one 
without having to make copies of all attributes?

class Derived (Base):
   def __init__ (self, base_object):
      # ( copy all attributes )
      ...

This looks expensive. Moreover __init__ () may not be available if it 
needs to to something else.

Thanks for suggestions

Frederic