How Can I Elegantly Iterate Through a List in Python in Specific-Sized Chunks?

Elegant Chunks: Iterating a List in Groups

Iterating over a list in specific-sized chunks can be a common task in Python programming. If the list contains elements to be processed in predefined groups, the typical approach might resemble the provided code:

for i in range(0, len(ints), 4):
    # Placeholder operation for illustrative purposes
    foo += ints[i] * ints[i + 1] + ints[i + 2] * ints[i + 3]

While this approach may fulfill the functional requirement, it can feel rather clunky and un-Pythonic. This article delves into a more elegant and idiomatic solution using a custom generator function:

def chunker(seq, size):
    return (seq[pos:pos + size] for pos in range(0, len(seq), size))

This generator function, chunker, elegantly splits the input sequence into chunks of the specified size, providing a streamlined way to iterate over them. The generator expression within chunker yields each chunk, starting from the beginning of the sequence and advancing by the chunk size until it reaches or surpasses the end of the sequence.

Here's an example demonstrating the versatility of the chunker function:

text = "I am a very, very helpful text"

for group in chunker(text, 7):
   print(repr(group),)

Output:

'I am a ' 'very, v' 'ery hel' 'pful te' 'xt'

This example chunks the text string into groups of 7 characters each. Similarly, it can be used with any type of sequence, including lists of animals or even arbitrary data structures.

In Python 3.12 and later, the chunker function can be further simplified using the itertools.tee() function:

from itertools import tee

def chunker(seq, size):
    a, b = tee(seq, 2)
    return (list(islice(a, i, None, size)) for i in range(size))

This variation of the function avoids creating an intermediate list and operates directly on the input sequence, highlighting the power of Python's built-in functions for working with iterables.

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