Iterate over a ‘window’ of adjacent elements in Python

Question

This is more a question of elegance and performance rather than “how to do at all”, so I\'ll just show the code:

def iterate_adjacencies(gen, fill=0, size=2,         


        

Answer 1

This is my version that fills, keeping the signature the same. I have previously seen the itertools recipe, but did not look at it before writing this.

from itertools import chain
from collections import deque

def ia(gen, fill=0, size=2, fill_left=True, fill_right=False):
    gen, ssize = iter(gen), size - 1
    deq = deque(chain([fill] * ssize * fill_left,
                      (next(gen) for _ in xrange((not fill_left) * ssize))),
                maxlen = size)
    for item in chain(gen, [fill] * ssize * fill_right):
        deq.append(item)
        yield deq

Edit: I also didn't see your comments on your question before posting this.

Edit 2: Fixed. I had tried to do it with one chain but this design needs two.

Edit 3: As @senderle noted, only use it this as a generator, don't wrap it with list or accumulate the output, as it yields the same mutable item repeatedly.