How to loop through all but the last item of a list?

if you meant comparing nth item with n+1 th item in the list you could also do with

>>> for i in range(len(list[:-1])):
...     print list[i]>list[i+1]

note there is no hard coding going on there. This should be ok unless you feel otherwise.

the easiest way to compare the sequence item with the following:

for i, j in zip(a, a[1:]):
     # compare i (the current) to j (the following)

If you want to get all the elements in the sequence pair wise, use this approach (the pairwise function is from the examples in the itertools module).

from itertools import tee, izip, chain

def pairwise(seq):
    a,b = tee(seq)
    b.next()
    return izip(a,b)

for current_item, next_item in pairwise(y):
    if compare(current_item, next_item):
        # do what you have to do

If you need to compare the last value to some special value, chain that value to the end

for current, next_item in pairwise(chain(y, [None])):

for x in y[:-1]

If y is a generator, then the above will not work.