On Wed, Dec 11, 2019 at 9:48 PM Tim Peters <tim.pet...@gmail.com> wrote:
> [Tim]
> >> Every suggestion here so far has satisfied that, if S is a non-empty
> set,
> >>
> >> assert next(iter(S)) is first(S)
> >>
> >> succeeds. That is, `first()` is _defined_ by reference to iteration
> >> order. It's "the first" in that order (hence the name).
>
> [Stephen J. Turnbull <turnbull.stephen...@u.tsukuba.ac.jp>]
> > The problem I'm concerned with is that sometimes users' definitions of
> > words differ from a computer language's definitions of words. That's
> > why I used the word "natural", which doesn't really have much to do
> > with the way a computer language defines things, but frequently
> > features in human thought.
> >
> > Whether that potential difference matters here is an empirical
> > question.
> >
> > Theoretically, I can say "Explicit is better than implicit."
> > I.e., the call to 'iter' tells us exactly what order is being used.
>
> But hasn't it already been settled by experience? There is nothing
> unique about `first(set)` implicitly appealing to iteration order. A
> set passed as the iterable to _any_ itertools function does exactly
> the same:
>
> >>> import itertools
> >>> list(itertools.zip_longest(set("abcde"), range(5))) # can vary from
> run to run
> [('a', 0), ('e', 1), ('c', 2), ('d', 3), ('b', 4)]
> >>> list(itertools.compress(set("abcde"), [1]*5)) # but is consistent
> within a run
> ['a', 'e', 'c', 'd', 'b']
> >>> list(itertools.takewhile(lambda x: True, set("abcde")))
> ['a', 'e', 'c', 'd', 'b']
>
> So do, e.g., some builtins:
>
> >>> list(map(ord, set("abcde")))
> [97, 101, 99, 100, 98]
> >>> [ord(ch) for ch in set("abcde")]
> [97, 101, 99, 100, 98]
>
>
> > That's *my* opinion in this case, and I don't hold *you* to it just
> > because I'm quoting you. (I am amused, though.)
>
> I just don't see the potential for "new" bafflement if itertools.first
> works exactly the same way as itertools.anything_else _has_ worked, in
> this respect, all along. Give users some credit. Programming is
> baffling, period, at first. But to those who persist, nothing becomes
> truly unbearable ;-)
>
I'm also sure the docs will say "Returns the first item yielded by the
iterable." That last word is a dead give-away on how the choice will be
made on any collection, Sequence or not. 😉 (Doubly true if this goes into
itertools.)
There's also the contingency of users who will think of the question "how
would this function think of what "first" is for non-order collections?"
will simply think "iterator" and be done with thinking.
IOW I understand the desire to have a function that is fully
self-explanatory, but I view take() as more ambiguous as it doesn't say
where you will take form (e.g. are you going to treat a list as a deque or
a stack?), but first() has a clear understanding the instant you think
about this operating on iterables (which is as universal of a data
structure concept across collection types as we have).
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