Py2.3: Feedback on Sets (fwd)

[Alex Martelli]

David Mertz wrote:
   ...
> Raymond Hettinger also wrote:
> |from sets import Set
> |def powerset(iterable):
> |    data = list(iterable)
> |    for i in xrange(2**len(data)):
> |        yield Set([e for j,e in enumerate(data) if i&(1<<j)])
> 
> Hmmm...  I should have checked the docs first.  A sample implementation
> obviously helps.  That said, this isn't REALLY an implementation of
> powerset.  It returns an iterator, not a set.  Now, sure... an iterator
> is a BETTER thing to get, for lots of reasons.  But I'm not sure it
> lives up to the function name.

Surely writing

def therealpowerset(iterable):
    return Set(powerset(iterable))

(or just inlining the Set call) isn't beyond the abilities of most
prospective users.  Just like one calls list(x) on any iterable x
if one needs specifically a list, so does one call Set(x) if one
needs specifically a set.  Sure, the name is debatable, and maybe
'subsetsof' would be neater.  But I think this is quibbling.

IMHO, one 'real' issue with this function is that it behaves strangely
(to me) when iterable has duplicated elements -- namely, the
resulting iterator also has duplications.  Changing the single
statement that is currently:
    data = list(iterable)
into
    data = Set(iterable)
would make duplications in 'iterable' irrelevant instead.



Alex