On 23/05/2020 05:48, David Mertz wrote:
On Sat, May 23, 2020, 12:26 AM Steven D'Aprano
Obviously not all such key functions are that simple and you may
need to write a helper function, but the same applies to filter.
I like the key function much better than the predicate. In large part
that's because as soon as you say predicate, I think filter.
Particularly if I care about laziness in not looking through extra items.
If you wanted everything matching a predicate, using a comprehension
just seems more obvious. It could be lazy with a generator
comprehension, not them you need next() to get the first.
Key= has the obvious parallel with sorted() and friends. Even then, a
function similar to sorted() feels more general than a method on lists
only.
I.e.
index_of(needle, haystack, key=func)
I'm not sure where that would live exactly, maybe itertools. I think
you were on my side in believing an import from standard library is
not a huge burden.
I think if such a function existed, I'd want another argument to match
n != 1 results. But then it gets ugly because one index is an integer,
and multiple indices are some sort of collection.
Sounds like a list comprehension: [ needle for needle in haystack if
func(needle) ]
So maybe one is best...
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