[Python-ideas] Batching/grouping function for itertools

[Amber Yust]

So does zip if the items are of unequal length, and the two code examples I
provided (the one using zip and the long-form one) are equivalent.

On Sun Dec 08 2013 at 9:49:56 AM, Mathias Panzenböck <
grosser.meister.morti at gmx.net> wrote:

> On 12/08/2013 05:44 AM, Amber Yust wrote:
> > After seeing yet another person asking how to do this on #python (and
> having needed to do it in the past myself), I'm
> > wondering why itertools doesn't have a function to break an iterator up
> into N-sized chunks.
> >
> > Existing possible solutions include both the "clever" but somewhat
> unreadable...
> >
> >      batched_iter = zip(*[iter(input_iter)]*n)
> >
> > ...and the long-form...
> >
> >      def batch(input_iter, n):
> >          input_iter = iter(input_iter)
> >          while True:
> >              yield [input_iter.next() for _ in range(n)]
> >
>
> This function drops items if the length of the input sequence is not a
> multiple of n. Fix:
>
>         def batch(it, n):
>                 it = iter(it)
>                 while True:
>                         slice = []
>                         for _ in range(n):
>                                 try:
>                                         slice.append(it.next())
>                                 except StopIteration:
>                                         if slice:
>                                                 yield slice
>                                         return
>                         yield slice
>
> > There doesn't seem, however, to be one clear "right" way to do this.
> Every time I come up against this task, I go back
> > to itertools expecting one of the grouping functions there to cover it,
> but they don't.
> >
> > It seems like it would be a natural fit for itertools, and it would
> simplify things like processing of file formats that
> > use a consistent number of lines per entry, et cetera.
> >
> > ~Amber
> >
>
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