Converting a flat list to a list of tuples

Bengt Richter bokr at oz.net
Wed Nov 23 13:12:02 CET 2005


On Wed, 23 Nov 2005 09:54:46 +0100, "Fredrik Lundh" <fredrik at pythonware.com> wrote:

>Bengt Richter wrote:
>
>> >Though it looks nice, it's an implementation dependant solution. What if
>> >someone changes zip to fetch the second item first?
>>
>> That would be a counter-intuitive thing to do. Most things go left->right
>> in order as the default assumption.
>
>it's not only the order that matters, but also the number of items
>read from the source iterators on each iteration.
>
Not sure I understand.

Are you thinking of something like lines from a file, where there might be
chunky buffering? ISTM that wouldn't matter if the same next method was called.
Here we have multiple references to the same iterator. Isn't e.g. buiding
a plain tuple defined with evaluation one element at a time left to right?
So an iterator it = xrange(4) can't know that it's being used in a context
like (it.next(), it.next()), so why should zip be any different? Zip _is_ building
tuples after all, and it's perfectly clear where they are coming from (or am
I missing something?) Why not left to right like a normal tuple?

Regards,
Bengt Richter



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