On Nov 14, 2013, at 7:47, אלעזר email@example.com wrote:
2013/11/14 Masklinn firstname.lastname@example.org:
On 2013-11-14, at 16:05 , Steven D'Aprano email@example.com wrote:
Aside: am I the only one who wishes there was a functools.rpartial, that binds from the right instead of the left?
I’ve wanted this as well. Or the ability to somehow “fill holes”. Scala- or Clojure-type parse transforms are pretty neat for that (write the call with holes/placeholders, the call is deferred as a function taking arguments to fill the placeholders)
Examples of Scala have already been provided, in Clojure it’s an explicit reader form:
# (foo 1 2 %)
This example doesn't actually show rpartial--but it's enough to make it obvious to anyone how you'd do that in Clojure, so that's ok.
is equivalent (and expanded) to
(fn [arg] (foo 1 2 arg))
Ellipsis seems suitable for the latter:
sub5 = partial(sub, ..., 5)
(At the expense of giving up the abitily to pass ellipsis to partial functions).
I don't know why, but to me that strongly implies that I'm binding argument -1 (after 0 or more arguments, or maybe 1 or more), rather than argument 2 (after exactly 1).
But that's not necessarily a bad thing. But if other people expect it to bind 2, they'll be surprised when they try it on a 3-argument (or variable-argument) function.
(And yes, I realize that mixing 1-based arg counting with python negative indices is potentially confusing. I don't think it's confusing in this particular case, but in, say, documentation for a stdlib function it could be.)