PEP 218 Re: ANN: set-0.1 module available

[Roman Suzi]

On Fri, 17 May 2002, James J. Besemer wrote:

> Fernando PИrez wrote:
> 
> > I beg to differ. Mathematically, there's nothing in the idea of a set that
> > makes it immutable. I know that Python is not a mathematics-only language,
> > but much of the cleanliness of its design does come from following abstract
> > ideas as much as is reasonable. And enforcing immutability on a set is one
> > hell of a breakage for an object as basic to many mathematical ideas as a set
> > is.
> 
> I beg to differ.  Mathematically, there's no notion of assignment like we have in
> programming.  From a traditional mathematics view " x = x + 1" is a nonsensical
> statement.  At best it's a contradiction in terms.  In Mathematics, you don't
> have assignment that can be done over and over.  You can only make statements
> about equality or inequality.  At bottom all mathematics is defined in terms of
> sets and predicates about sets.

It is right. But if you look into applied math journals, people
communicate algorithms in a pseudolanguage where sets are 
widely used. It could be nice if Python supported such things closer.

> In the context of mathematics I would argue that ALL objects are
> immutable.  When you say "2 + 3 = 5", the 2 and the 3 don't cease to
> exist.  Numbers are immutable.  Similarly, when you say B union C you
> are defining a third, new set, composed of the union of the first two.  
> The first two don't go away.  They continue to exist (necessarily) to
> maintain the definition of the result.  You don't destroy or reuse the
> previous ones.

Sincerely yours, Roman A.Suzi
-- 
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