On 28 Apr 2010, at 12:48 , cool-RR wrote:
On Tue, Apr 27, 2010 at 12:12 AM, George Sakkis <george.sakkis@gmail.com>wrote:
On Mon, Apr 26, 2010 at 11:41 PM, cool-RR <cool-rr@cool-rr.com> wrote:
On Mon, Apr 26, 2010 at 11:34 PM, George Sakkis <george.sakkis@gmail.com
wrote:
On Mon, Apr 26, 2010 at 11:18 PM, cool-RR <cool-rr@cool-rr.com> wrote:
On Mon, Apr 26, 2010 at 11:13 PM, Xavier Ho <contact@xavierho.com> wrote:
On Tue, Apr 27, 2010 at 7:10 AM, cool-RR <cool-rr@cool-rr.com>
wrote:
> > Just something small that I thought of, and I haven't thought about > this > deeply at all, so maybe this is way wrong. But: What about adding a > `Reversable` next to all the `Iterable` and `Container` and stuff?
You mean there is something Iterable we can't reverse by doing [::-1] or calling reversed() ? This idea feels a bit too general to be useful. Any rationales?
Cheers, Xav
As far as I know, iterables are generally not reversable. Try defining a simple iterator, like a class with just an `__iter__` function, and run `reversed` on it. You get `TypeError: argument to reversed() must be a sequence`. (Which by the way is a bad error message.) Am I missing something?
So what should reversed() (or a new Reversable()) return for, say, itertools.count() ?
By the way, comp.lang.python [1] or the tutor mailing list [2] are more appropriate than python-ideas for asking questions "you haven't thought about deeply at all".
George
[1] http://mail.python.org/mailman/listinfo/python-list [2] http://mail.python.org/mailman/listinfo/tutor
I'm not really understanding you, George. Am I getting something very wrong here? When you put `itertools.count()` into `reversed()`, you get an error, like you should, because it's not a sequence and it doesn't define `__reversed__`. So it's not a reversable object. I'm proposing to have a `Reversable` similar to `Iterable`, which checks the existence of `__reversed__` instead of `__iter__`.
Sorry, it wasn't obvious (to me at least) that you were talking about the abstract classes under the collections module, and in your second post you implied (again, that was my understanding at any rate) that defining a class with just an __iter__ should be acceptable by `reversed` instead of raising a TypeError.
On the other hand a collections.Reversable abstract class that checks specifically for __reversed__ sounds quite reasonable.
George
Does anyone else care to express their opinion about the Reversable suggestion?
Ram.
I'm not quite sure of the point/use case for the feature, but that's about it.