[Python-Dev] Re: PEP 218 (sets); moving set.py to Lib

[Guido van Rossum]

> [snip]
> > no hope that this will ever complete in finite time, but does that
> > mean it shouldn't start?  I could write 1L<<e and avoid the issue, but
> > then I'd be paying for long ops that I'll only ever need in a case
> > that's only of theoretical importance.
> 
> How about lazy sets? E.g. a CartesianProduct could delegate to its two
> underlying (concrete) sets when checking for membership, and a
> PowerSet could perform individual member cheks for each element in a
> given subset... Etc.

Have you got a use case for membership tests of a cartesian product?

> I guess this might be too specific for the library -- subclassing
> ImmutableSet and overriding the accessors shouldn't be too hard...
> 
> (The nice thing about including it in the library is that you could
> produce these things as results from operations on Set and
> ImmutableSet, e.g. 2**some_set could give a power set or whatever...)

Use case?

--Guido van Rossum (home page: http://www.python.org/~guido/)