What is the most "pythonic" way to iterate over a list in chunks?
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 xrange(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?
Modified from the recipes section of Python's itertools docs:
from itertools import izip_longest
def grouper(iterable, n, fillvalue=None):
args = [iter(iterable)] * n
return izip_longest(*args, fillvalue=fillvalue)
Example
In pseudocode to keep the example terse.
grouper('ABCDEFG', 3, 'x') --> 'ABC' 'DEF' 'Gxx'
Note: izip_longest is new to Python 2.6. In Python 3 use zip_longest .
def chunker(seq, size):
return (seq[pos:pos + size] for pos in xrange(0, len(seq), size))
Simple. Easy. Fast. Works with any sequence:
text = "I am a very, very helpful text"
for group in chunker(text, 7):
print repr(group),
# 'I am a ' 'very, v' 'ery hel' 'pful te' 'xt'
print '|'.join(chunker(text, 10))
# I am a ver|y, very he|lpful text
animals = ['cat', 'dog', 'rabbit', 'duck', 'bird', 'cow', 'gnu', 'fish']
for group in chunker(animals, 3):
print group
# ['cat', 'dog', 'rabbit']
# ['duck', 'bird', 'cow']
# ['gnu', 'fish']
我是一个粉丝
chunkSize= 4
for i in xrange(0, len(ints), chunkSize):
chunk = ints[i:i+chunkSize]
# process chunk of size <= chunkSize
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