Iterate over all pairs of consecutive items in a list [duplicate]

Answer 1

A simple means to do this without unnecessary copying is a generator that stores the previous element.

def pairs(iterable):
    """Yield elements pairwise from iterable as (i0, i1), (i1, i2), ..."""
    it = iter(iterable)
    try:
        prev = next(it)
    except StopIteration:
        return
    for item in it:
        yield prev, item
        prev = item

Unlike index-based solutions, this works on any iterable, including those for which indexing is not supported (e.g. generator) or slow (e.g. collections.deque).