iterating and detecting the last

[Skaperen]

i am iterating over a list (or tuple). for each item except the last item i need to do a specific thing. for the last item i need to do something different. the solution i am thinking about is to get the initial len() of the list and count as the iterating proceeds. if the counting is up, i detect the last when the count equals the length. another way is iterating over range(len(seq)-1) and indexing the sequence like:

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for x in range(len(seq)-1):      foo(seq[x]) bar(seq[-1])

there are many ways to do this. which would be the best? which would be most pythonic?

[Yoriz]

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items = [1, 2, 3, 4]   for item in items[:-1]:     print(item) print(f"last item = {items[-1]}")

Output:
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2
3
last item = 4

[bowlofred]

If you know it's a sequence (which list and tuples are), I'd just iterate over obj[:-1].

If it's something that isn't a sequence (like a generator), then you could just stick the current object in a cache and operate on it after you read the next item.

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for element in seq[:-1]:     foo(element) bar(seq[-1])

or:

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i = iter(obj) cache = next(i) for item in i:     foo(cache)     cache = item bar(cache)

[Gribouillis]

The cache strategy is also implemented in more_itertools.peekable()

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for item in (p := peekable(iterable)):     if not p:         print(f"Item {item} is the last one")     else:          print("Not the last item")