On Thu, Jan 13, 2011 at 3:10 PM, Masklinn <masklinn@masklinn.net> wrote:
(c) Unlike ML, you can write (a, b) = [1, 2] or generally a, b = any_iterable It is useful for unpacking to depend on the iterable protocol rather than the exact type of the right-hand side. This is a nicety that ML-like languages don't bother with, afaik. In no small part because, in ML-type languages (or more generally in functional languages, Erlang could hardly be called an ML-like language)
On 2011-01-13, at 21:11 , Jason Orendorff wrote: lists (or more generally sequences) and tuples are very different beasts and entirely incompatible.
Well, sure, as far as tuples go. But the point I was making was more general. Python has a notion of "iterable" which covers many types, not just "list". The iterable protocol is used by Python's for-loops, sorted(), str.join() and so on; it's only natural for unpacking assignment to use it as well. As far as I know, most ML languages don't have that notion.* So Python has a reason for this asymmetry that those languages don't have. -j *Haskell, to be sure, has several typeclasses that generalize List, but for whatever reason it is List, and not any of the generalizations, that is baked into the language.