l=[1,2,3]
for item in l:
    if item==2:
        get_previous(l,item)

def neighborhood(iterable):
    iterator = iter(iterable)
    prev_item = None
    current_item = next(iterator)  # throws StopIteration if empty.
    for next_item in iterator:
        yield (prev_item, current_item, next_item)
        prev_item = current_item
        current_item = next_item
    yield (prev_item, current_item, None)

for prev,item,next in neighborhood(l):
    print prev, item, next

l=[1,2,3]
for i,j in zip(l, l[1:]):
    print i, j

l=[1,2,3]
for i,item in enumerate(l):
    if item==2:
        get_previous=l[i-1]
        print get_previous

>>>1

import collections, itertools

def window(it, winsize, step=1):
    """Sliding window iterator."""
    it=iter(it)  # Ensure we have an iterator
    l=collections.deque(itertools.islice(it, winsize))
    while 1:  # Continue till StopIteration gets raised.
        yield tuple(l)
        for i in range(step):
            l.append(it.next())
            l.popleft()

>>> list(window([1,2,3,4,5],3))
[(1, 2, 3), (2, 3, 4), (3, 4, 5)]

l= range(10)
# Print adjacent numbers
for cur, next in window(l + [None] ,2):
    if next is None: print "%d is the last number." % cur
    else: print "%d is followed by %d" % (cur,next)

> easy_install Tempita
> python
>>> from tempita import looper
>>> for loop, i in looper([1, 2, 3]):
...     print loop.previous, loop.item, loop.index, loop.next, loop.first, loop.last, loop.length, loop.odd, loop.even
...
None 1 0 2 True False 3 True 0
1 2 1 3 False False 3 False 1
2 3 2 None False True 3 True 0

some_list = ["bob", "bill", "barry"]

for item in some_list:
    print "Item - " + item
    if some_list.index(item) != len(some_list) -1:
        next_item = some_list[some_list.index(item) + 1]
        print "Next item -", next_item
    else:
        print "Next item does not exist!"

for itemIndex, item in enumerate(l):
    if itemIndex>0:
        previousItem = l[itemIndex-1]
    else:
        previousItem = None

previous = None
for item in someList:
    if item == target: break
    previous = item
# previous is the item before the target

queue = []
for item in someList:
    if item == target: break
    queue .append( item )
    if len(queue ) > n: queue .pop(0)
if len(queue ) < n: previous = None
previous = previous[0]
# previous is *n* before the target

l=[1,2,3]
for index in range(len(l)):
    if l[index]==2:
        l[index-1]

def get_previous(l, item):
    idx = l.find(item)
    return None if idx == 0 else l[idx-1]

for idx in range(len(l)):
    item = l[idx]
    if item == 2:
        l[idx-1]