[Python-Dev] Re: PEP 218 (sets); moving set.py to Lib
Guido van Rossum
Tue, 20 Aug 2002 20:37:49 -0400
> > I am still perplexed that I received *no* feedback on the sets
> > module
> As I previously said, I feel comfortable with what I read and saw.
> I'd probably have to use sets for having more circumstantiated
> Unless you offer the source on c.l.py and ask for more users' opinions?
Last time I tried that it turned out a bad idea. I prefer feedback
over a flame war.
> Maybe some people would have preferred to see more usual notation,
> like `+' for union and `*' for intersection, rather than `or' and
> `and'? There are tiny pros and cons in each direction. For one,
> I'll gladly use what is available, I'm not really going to crusade
> for either notation...
Um, the notation is '|' and '&', not 'or' and 'and', and those are
what I learned in school. Seems pretty conventional to me (Greg
Wilson actually tried this out on unsuspecting newbies and found that
while '+' worked okay, '*' did not -- read the PEP).
But yes, this is decent feedback (with good enough arguments, Greg's
conclusion might even be overturned).
> Should there be special provisions for Sets to interoperate
> magically with lists or iterators? Lists and iterators could be
> considered as ordered sets with duplicates allowed. Even if it
> could be tinily useful, it is surely not difficult to explicitly
> "cast" lists and iterators using the `Set' constructor. It is
> already easy to build an iterator or a list out of a set.
You can do an in-place union of a Set and a sequence or iterable with
set.update(seq). If you want intersection or a difference, or your
set is immutable, you'd have to cast the sequence to a set. What's
the use case?
Which brings me to another open issue.
set.update(seq) and set.add(element) have a provision to transform the
inserted element(s) to an ImmutableSet if needed. Should the
constructor do the same?
> Criticism? OK! What about supporting infinite sets? :-) Anything else?
> Hmph! The module doc-string has the word "actually" with three `l'! :-)
Not any more, thanks to Raymond Hettinger. :-)
--Guido van Rossum (home page: http://www.python.org/~guido/)