enhancing/wrapping an existing instance of a duck

[Neville Dempsey]

Basically I have an existing (maybe a rather large and complicated
(existing) instance) that
I want to add new member to.

Cheers
N

Hacks/attempts follow:

from math import sqrt

############ try2 ############
duck_obj = [ i*i for i in range(25) ] # OR a large sparse matrix

# I "want" to an a useful property, eg length, and retain the ducks
existing properties.
# I COULD try...
setattr(duck_obj,"length",lambda: sqrt(sum(*duck_obj)))
print duck_obj.length() # returns 70
duck_obj[0]=70+71
print duck_obj.length() # returns 71

############ try2 ############
# **BUT** I'd rather encapsulate a the original instance somehow.

# I presume that I could define a class to do this somehow?
duck_obj = [ i*i for i in range(25) ] # OR a LargeSparseMatrix()

dec = Vec(duck_obj) ???
print dec.length() # returns 70
duck_obj[0]=70+71 # original "large and complicated duck instance"
print dec.length() # returns 71

Any hints on how I need to define Vec so that any kind of duck_obj can
be decorated/wrapped/encapsulated.