Simple exercise

[Peter Otten]

Ian Kelly wrote:

> On Mon, Mar 14, 2016 at 9:06 AM, Oscar Benjamin
> <oscar.j.benjamin at gmail.com> wrote:
>> On 14 March 2016 at 14:35, Rick Johnson <rantingrickjohnson at gmail.com>
>> wrote:
>>>
>>> I would strongly warn anyone against using the zip function
>>> unless
>> ...
>>> I meant to say: absolutely, one hundred percent *SURE*, that
>>> both sequences are of the same length, or, absolutely one
>>> hundred percent *SURE*, that dropping values is not going to
>>> matter. For that reason, i avoid the zip function like the
>>> plague. I would much rather get an index error, than let an
>>> error pass silently.
>>
>> I also think it's unfortunate that zip silently discards items. Almost
>> always when I use zip I would prefer to see an error when the two
>> iterables are not of the same length.
> 
> It's sometimes very useful, though. For example on multiple occasions
> I've taken advantage of the fact that enumerate(x) is equivalent to
> zip(itertools.count(), x). If zip raised an error then that would only
> be possible using islice, and then only if the length is known in
> advance.
> 
> Also, in order for zip to know that the lengths are not equal, it
> would have to try to read one additional item from the longer
> iterable. That's rather unfortunate if it's an iterator and you're
> hoping to catch the exception and then use the rest of the iterator
> for something else.

That's a problem you may run into with the current zip(), too -- unless you 
know that the first is the shortest iterator:

>>> from itertools import count
>>> indices = count()
>>> for items in "abc", "def", "gh":
...    list(zip(indices, items))
... 
[(0, 'a'), (1, 'b'), (2, 'c')]
[(4, 'd'), (5, 'e'), (6, 'f')]
[(8, 'g'), (9, 'h')]

I'm with Oscar here, raising an exception would be the better default; the 
current implementation could have been made available as 
itertools.zip_shortest().