itertools.izip brokeness

[Bengt Richter]

On 5 Jan 2006 14:34:39 -0800, rurpy at yahoo.com wrote:

>
>Bengt Richter wrote:
>> On 5 Jan 2006 15:48:26 GMT, Antoon Pardon <apardon at forel.vub.ac.be> wrote:
>>
>> >On 2006-01-04, rurpy at yahoo.com <rurpy at yahoo.com> wrote:
>> >><rurpy at yahoo.com> wrote:
>> >>> But here is my real question...
>> >>> Why isn't something like this in itertools, or why shouldn't
>> >>> it go into itertools?
>> >>
>> >>
>> >>   4) If a need does arise, it can be met by __builtins__.map() or by
>> >>      writing:  chain(iterable, repeat(None)).
>> >>
>> >> Yes, if youre a python guru.  I don't even understand the
>> >> code presented in this thread that uses chain/repeat,
>> >
>> >And it wouldn't work in this case. chain(iterable, repeat(None))
>> >changes your iterable into an iterator that first gives you
>> >all elements in the iterator and when these are exhausted
>> >will continue giving the repeat parameter. e.g.
>> >
>> >  chain([3,5,8],repeat("Bye")
>> >
>> >Will produce  3, 5 and 8 followed by an endless stream
>> >of "Bye".
>> >
>> >But if you do this with all iterables, and you have to
>> >because you don't know which one is the smaller, all
>> >iterators will be infinite and izip will never stop.
>>
>> But you can fix that (only test is what you see ;-) :
>>
>>  >>> from itertools import repeat, chain, izip
>>  >>> it = iter(lambda z=izip(chain([3,5,8],repeat("Bye")), chain([11,22],repeat("Bye"))):z.next(), ("Bye","Bye"))
>>  >>> for t in it: print t
>>  ...
>>  (3, 11)
>>  (5, 22)
>>  (8, 'Bye')
>>
>> (Feel free to generalize ;-)
>
>Which just reinforces my original point: if leaving
>out a feature is justified by the existence of some
>alternate method, then that method must be equally
>obvious as the missing feature, or must be documented
>as an idiom.  Otherwise, the justification fails.
>
>Is the above code as obvious as
>  izip([3,5,8],[11,22],sentinal='Bye')?
>(where the sentinal keyword causes izip to iterate
>to the longest argument.)
>
You are right. I was just responding with a quick fix to the
problem Antoon noted.
For a more flexible izip including the above capability, but
also abble to do the default izip with a capability of continuing iteration
in the above mode after the normal izip mode stops, see izip2.py in my other
post in this thread.

Regards,
Bengt Richter