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]))

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