itertools.izip brokeness

bonono at bonono at
Tue Jan 3 06:31:45 EST 2006

Paul Rubin wrote:
> > I think you need to use map(None,...) which would not drop anything,
> > just None filled. Though you don't have a relatively lazy version as
> > imap(None,...) doesn't behave like map but a bit like zip.
> I don't understand what you mean by this?  None is not callable.

zip([1,2,3],[4,5])  gives [(1,4),(2,5)]

map(None,[1,2,3],[4,5]) gives [(1,4),(2,5),(3,None)]

So the result of map() can be filtered out for special processing. Of
course, your empty/sentinel filled version is doing more or less the
same thing.

> How about this (untested):
>   def myzip(iterlist):
>     """return zip of smaller and smaller list of iterables as the
> individual iterators run out"""
>     sentinel = object()  # unique sentinel
>     def sentinel_append(iterable):
>        return itertools.chain(iterable, itertools.repeat(sentinel))
>     for i in itertools.izip(map(sentinel_append, iterlist)):
>        r = [x for x in if x is not sentinel]
>        if r: yield r
>        else: break

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