[Guido]
> ...
> Similarly, there is already a spelling of first() (or close enough) that
> raises: 1-arg next().
> If 1-arg first() would also raise, it would fail the rule "similar things
> should be spelled
> similarly, and different things should be spelled differently".
The "... unless you're Dutch" part of the Zen may be at work here ;-)
Under your semantics for first(),
first(iterator)
next(iterator)
look darned near identical, but act very differently if the iterator
is exhausted: the second raises StopIteration, while the former
returns None. The alternative proposal is that they both raise an
exception if the iterator is exhausted: then they look much the same
_and_ act much the same.
Likewise under the alternative if a default is explicitly given to both.
It's true that dict.get(key) returns None too, but (a) that's a method
rather than a function; and, (b) `first` and `next` are very closely
related to each other, but not to any dict methods; and, (c)
next(iterable) and dict.get(key) already look kinda similar but
already did quite different things in their respective end cases
("iterator already exhausted" and "key not present").
> I am not making this rule up -- it's an old design principle that Lambert
> Meertens
> used for ABC, Python's predecessor. It just didn't make it in the Zen of
> Python,
> unless you want to interpret "there should be one [...] way to do it" as its
> spiritual
> descendant.
Or unless you want to add it now as the mysterious 20th aphorism
that's been waiting to be revealed :-)
> IMO "one raises StopIteration and one raises ValueError" is not enough to
> warrant two different ones,
Two different _whats_?
> nor is "one calls iter() and the other doesn't." But "one raises and the other
> doesn't" is a significant enough difference (as the example of dict.get()
> shows).
Well, ya: that's a very significant difference, so doesn't the
Meertens Principle suggest that "one raises but the other doesn't"
should _not_ look identical?
>
> FWIW I think "first()" is a fine name to get one element from a set -- it's
> not likez
>. the iteration order is a secret, and it's not called "lowest". The other
>schemes to
> get one item out of a set in O(1) time will return the same element, since
> the only
> sensible way to do it is to iterate and stop after one iteration.
Wholly agreed there. `first()` may or may not be self-evident at
first glance, but the meaning becomes obvious and impossible to forget
after the first minor effort to grasp it.
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