Python - Way to distinguish between item index in a list and item's contents in a FOR loop?

Question

For instance, if I wanted to cycle through a list and perform some operation on all but the final list entry, I could do this:

z = [1,2,3,4,2]
for item in z:
    if item != z[-1]:        
        print z.index(item)

But instead of getting the output "...0 1 2 3," I'd get "...0 2 3."

Is there a way to perform an operation on all but the last item in a list (when there are IDENTICAL items in the list) without using a "for x in range (len(list) - 1)" sort of solution? I.e., I want to keep using "for item in list."

Many thanks!

Answer 1

for index, item in enumerate(your_list):
    do_something

Answer 2

you could use:

for index, item in enumerate(z):
    if index != len(z)-1:
        print index

Answer 3

[z.foo() for z in z[:-1]

Answer 4

Use a slice:

for item in z[:-1]:
    # do something

Answer 5

def all_but_last(iterable):
    iterable= iter(iterable)

    try: previous= iterable.next()
    except StopIteration: return

    for item in iterable:
        yield previous
        previous= item

Put it in a module and use it wherever you need it.

In your case, you'd do:

for item in all_but_last(z):