How Can I Iterate Over Pairs or Groups of Elements in a Python List?

Iterating Over Every Two Elements in a List

In Python, iterating over a list often involves using a for loop or list comprehension. However, when you need to access every two elements together, the standard methods may not be sufficient.

To iterate over every pair of elements in a list, you can utilize the pairwise() implementation:

def pairwise(iterable):
    "s -> (s0, s1), (s2, s3), (s4, s5), ..."
    a = iter(iterable)
    return zip(a, a)

l = [1, 2, 3, 4, 5, 6]

for x, y in pairwise(l):
    print(f"{x} + {y} = {x + y}")

This function iterates through the list twice, pairing every element with the next one. It produces output similar to this:

1 + 2 = 3
3 + 4 = 7
5 + 6 = 11

For a more general solution, consider the grouped() function, which allows you to iterate over groups of n elements:

def grouped(iterable, n):
    "s -> (s0,s1,s2,...sn-1), (sn,sn+1,sn+2,...s2n-1), (s2n,s2n+1,s2n+2,...s3n-1), ..."
    return zip(*[iter(iterable)] * n)

for x, y in grouped(l, 2):
    print(f"{x} + {y} = {x + y}")

This function takes a list and a group size as arguments and returns an iterator that produces groups of elements. For example, calling grouped([1, 2, 3, 4, 5, 6], 3) would yield:

(1, 2, 3)
(4, 5, 6)

In Python 2, you can use izip instead of zip for compatibility purposes.

These methods provide efficient and flexible ways to iterate over elements in a list, allowing you to process them in pairs or groups as needed.

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