How to iterate the input over a particular size?

[Peter Otten]

Francesco Bochicchio wrote:

> Not sure I understood your question, but if you need just to plit a
> big list in sublists of no more than 9 elements, then you can do
> someting like:
> 
> def sublists(biglist, n ):
>         "Splits a big list in sublists of max n elements"
>         prev_idx = 0; res = []
>         for idx in xrange(n, len(biglist)+n, n ):
>                 res.append( biglist[prev_idx:idx] )
>                 prev_idx = idx
>         return res
> 
> I would not be surprised if somewhere in python standard library there
> is something like this (possibly better), but
> could not find anything.

A lazy alternative:

>>> from itertools import islice
>>> def chunks(items, n):
...     items = iter(items)
...     for first in items:
...             chunk = [first]
...             chunk.extend(islice(items, n-1))
...             yield chunk
...
>>> list(chunks(range(10), 3))
[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]]

One with lazy chunks:

>>> from itertools import chain, islice
>>> def chunks(items, n):
...     items = iter(items)
...     for first in items:
...             yield chain((first,), islice(items, n-1))
...
>>> [list(chunk) for chunk in chunks(range(10), 3)]
[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]]

Prior art by Duncan Booth:
http://mail.python.org/pipermail/python-list/2007-November/517993.html

Peter