What is the correct (or best) way to subclass the Python set class, adding a new instance variable?

Question

I\'m implementing an object that is almost identical to a set, but requires an extra instance variable, so I am subclassing the built-in set object. What is the best way to

Answer 1

For me this works perfectly using Python 2.5.2 on Win32. Using you class definition and the following test:

f = Fooset([1,2,4])
s = sets.Set((5,6,7))
print f, f.foo
f.foo = 'bar'
print f, f.foo
g = f | s
print g, g.foo
assert( (f | f).foo == 'bar')

I get this output, which is what I expect:

Fooset([1, 2, 4]) default
Fooset([1, 2, 4]) bar
Fooset([1, 2, 4, 5, 6, 7]) bar