How Can I Iterate Through a List in Python Using Pairwise or N-Tuple Grouping?

Performing Pairwise Iteration in Lists

Problem:

In a given list, iterate over the elements in pairs to perform a specific operation.

Implementation:

A Pythonic approach for pairwise iteration is to employ the pairwise() or grouped() functions:

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("{} + {} = {}".format(x, y, x + y))

This function zips the iterable with itself, resulting in pairs of elements.

Generalized Grouping:

To group elements in n-tuples, use the grouped() function:

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 instance, to iterate over triples from the list l above:

for x, y, z in grouped(l, 3):
    print("{} + {} + {} = {}".format(x, y, z, x + y + z))

Type Checking with Mypy:

For type checking in Python 3 with Mypy:

from typing import Iterable, Tuple, TypeVar

T = TypeVar("T")

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

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