Splitting a list into even size chunks in python?

Peter Otten __peter__ at web.de
Wed Mar 27 09:27:49 CET 2013

Norah Jones wrote:

> I have a list of arbitrary length, and I need to split it up into equal
> size chunks. There are some obvious ways to do this, like keeping a
> counter and two lists, and when the second list fills up, add it to the
> first list and empty the second list for the next round of data, but this
> is potentially extremely expensive.
> I was wondering if anyone had a good solution to this for lists of any
> length
> This should work:
>     l = range(1, 1000)
>     print chunks(l, 10) -> [ [ 1..10 ], [ 11..20 ], .., [ 991..999 ] ]
> I was looking for something useful in itertools but I couldn't find
> anything obviously useful.

Look again, for the grouper() recipe. For lists you can also use slicing:

>>> items
['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> n = 3
>>> [items[start:start+n] for start in range(0, len(items), n)]
[['a', 'b', 'c'], ['d', 'e', 'f'], ['g']]

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