Previous / current / next iterator in Python

pcniter.py

def previous_current_next(iterable):
	"""Make an iterator that yields an (previous, current, next) tuple per element.
 
	Returns None if the value does not make sense (i.e. previous before
	first and next after last).
	"""
	iterable=iter(iterable)
	prv = None
	cur = iterable.next()
	try:
		while True:
			nxt = iterable.next()
			yield (prv,cur,nxt)
			prv = cur
			cur = nxt
	except StopIteration:
		yield (prv,cur,None)
 
# Examples
print list(previous_current_next([]))
print list(previous_current_next([1]))
print list(previous_current_next([1,2]))
print list(previous_current_next([1,2,3]))

that is so useful Sir thank you so much :)

it doesnt work with python 3.5

AttributeError: 'list_iterator' object has no attribute 'next'

Instead you can use

def previous_current_next(iterable):
    """Make an iterator that yields an (previous, current, next) tuple per element.

    Returns None if the value does not make sense (i.e. previous before
    first and next after last).
    """
    iterable = iter(iterable)
    prv = None
    cur = iterable.__next__()
    try:
        while True:
            nxt = iterable.__next__()
            yield (prv, cur, nxt)
            prv = cur
            cur = nxt
    except StopIteration:
        yield (prv, cur, None)

how about just add prev and current as keywords to compliment next

In Python 3.5 you can also use next(iterable).