Why is dictionary.keys() a list and not a set?

[Christoph Zwerschke]

Alex Martelli wrote:

> An alternative theory, of course, is "God made the natural numbers; all
> else is the work of man" -- and that one is by a German, too (Kronecker,
> if I recall correctly).

Yes, it was Kronecker. But even natural numbers are usually constructed 
with sets using Peano's axioms.

 > The hope to found all of mathematics on set theory was primarily a
 > _British_ effort, as I see it (Russell and Whitehead), and failed a
 > long time ago... I'm not sure what, if anything, a mathematician of
 > today would propose as the foundational theory...

Perhaps "string theory" ;-) So probably strings should become the 
fundamental datatype in Python (immutable strings of course) :-)

> But OO really requires a different mindset, particularly when operating
> under a regime of "mutable" objects.  "A circle IS-AN ellipse" in
> Euclidean geometry... but inheriting Circle from Ellipse doesn't work in
> OO if the objects are changeable, since you can, e.g., change
> eccentricity in an Ellipse but not in a Circle...

Good example.

-- Christoph