# What is the most “pythonic” way to iterate over a list in chunks?

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I have a Python script which takes as input a list of integers, which I need to work with four integers at a time. Unfortunately, I don"t have control of the input, or I"d have it passed in as a list of four-element tuples. Currently, I"m iterating over it this way:

``````for i in range(0, len(ints), 4):
# dummy op for example code
foo += ints[i] * ints[i + 1] + ints[i + 2] * ints[i + 3]
``````

It looks a lot like "C-think", though, which makes me suspect there"s a more pythonic way of dealing with this situation. The list is discarded after iterating, so it needn"t be preserved. Perhaps something like this would be better?

``````while ints:
foo += ints[0] * ints[1] + ints[2] * ints[3]
ints[0:4] = []
``````

Still doesn"t quite "feel" right, though. :-/

Related question: How do you split a list into evenly sized chunks in Python?

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## What is the most "pythonic" way to iterate over a list in chunks? split: Questions

How do you split a list into evenly sized chunks?

By jespern

I have a list of arbitrary length, and I need to split it up into equal size chunks and operate on it. 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, e.g. using generators.

I was looking for something useful in `itertools` but I couldn"t find anything obviously useful. Might"ve missed it, though.

2632

Here"s a generator that yields the chunks you want:

``````def chunks(lst, n):
"""Yield successive n-sized chunks from lst."""
for i in range(0, len(lst), n):
yield lst[i:i + n]
``````

``````import pprint
pprint.pprint(list(chunks(range(10, 75), 10)))
[[10, 11, 12, 13, 14, 15, 16, 17, 18, 19],
[20, 21, 22, 23, 24, 25, 26, 27, 28, 29],
[30, 31, 32, 33, 34, 35, 36, 37, 38, 39],
[40, 41, 42, 43, 44, 45, 46, 47, 48, 49],
[50, 51, 52, 53, 54, 55, 56, 57, 58, 59],
[60, 61, 62, 63, 64, 65, 66, 67, 68, 69],
[70, 71, 72, 73, 74]]
``````

If you"re using Python 2, you should use `xrange()` instead of `range()`:

``````def chunks(lst, n):
"""Yield successive n-sized chunks from lst."""
for i in xrange(0, len(lst), n):
yield lst[i:i + n]
``````

Also you can simply use list comprehension instead of writing a function, though it"s a good idea to encapsulate operations like this in named functions so that your code is easier to understand. Python 3:

``````[lst[i:i + n] for i in range(0, len(lst), n)]
``````

Python 2 version:

``````[lst[i:i + n] for i in xrange(0, len(lst), n)]
``````

2632

If you want something super simple:

``````def chunks(l, n):
n = max(1, n)
return (l[i:i+n] for i in range(0, len(l), n))
``````

Use `xrange()` instead of `range()` in the case of Python 2.x

2632

Directly from the (old) Python documentation (recipes for itertools):

``````from itertools import izip, chain, repeat

"grouper(3, "abcdefg", "x") --> ("a","b","c"), ("d","e","f"), ("g","x","x")"
``````

The current version, as suggested by J.F.Sebastian:

``````#from itertools import izip_longest as zip_longest # for Python 2.x
from itertools import zip_longest # for Python 3.x
#from six.moves import zip_longest # for both (uses the six compat library)

"grouper(3, "abcdefg", "x") --> ("a","b","c"), ("d","e","f"), ("g","x","x")"
``````

I guess Guido"s time machine works‚Äîworked‚Äîwill work‚Äîwill have worked‚Äîwas working again.

These solutions work because `[iter(iterable)]*n` (or the equivalent in the earlier version) creates one iterator, repeated `n` times in the list. `izip_longest` then effectively performs a round-robin of "each" iterator; because this is the same iterator, it is advanced by each such call, resulting in each such zip-roundrobin generating one tuple of `n` items.

We hope this article has helped you to resolve the problem. Apart from What is the most “pythonic” way to iterate over a list in chunks?, check other split-related topics.

Want to excel in Python? See our review of the best Python online courses 2022. If you are interested in Data Science, check also how to learn programming in R.

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Marie Emmerson

Tallinn | 2022-12-02

split is always a bit confusing 😭 What is the most “pythonic” way to iterate over a list in chunks? is not the only problem I encountered. I am just not quite sure it is the best method

Cornwall Porretti

Berlin | 2022-12-02

Simply put and clear. Thank you for sharing. What is the most “pythonic” way to iterate over a list in chunks? and other issues with StackOverflow was always my weak point 😁. I am just not quite sure it is the best method

Jan Porretti

Texas | 2022-12-02

split is always a bit confusing 😭 What is the most “pythonic” way to iterate over a list in chunks? is not the only problem I encountered. I just hope that will not emerge anymore

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