On 07/12/2010 00:23, Steven D'Aprano wrote:
On Mon, 06 Dec 2010 13:13:40 -0800, Paul Rubin wrote:
It's really unfortunate, though, that Python 3 didn't offer a way to
peek at the next element of an iterable and test emptiness directly.
This idea of peekable iterables just won't die, despite the obvious flaws
in the idea.
There's no general way of telling whether or not a lazy sequence is done
except to actually generate the next value, and caching that value is not
appropriate for all such sequences since it could depend on factors which
have changed between the call to peek and the call to next.
If you want to implement a peek method in your own iterables, go right
ahead. But you can't make arbitrary iterables peekable without making a
significant class of them buggy.
Perhaps Python could use Guido's time machine to check whether the
sequence will yield another object in the future. :-)
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