Note that izip stops when any input sequence gets exhausted, so the last element of prevs will be ignored, which is correct - there's no such element that the last element would be its prev. finally izip is used to change 3 sequences into one sequence of triplets.There are now 3 independent sequences based on some_iterable that look like:.islice is used to make a sequence of all elements except the first, then chain is used to append a None to its end.chain links two sequences into one it's used here to append a single-element sequence to prevs.tee is used to efficiently create 3 independent iterators over the input sequence.No need to search again for the item in the sequence. This way you can just iterate over the sequence, and have the previous and next items available inside the loop. It'll work with any size list (because it doesn't copy the list), and with any iterable (files, sets, etc). Item is now tomato next is None previous is kiwi Item is now kiwi next is tomato previous is apple Item is now apple next is kiwi previous is orange Item is now orange next is apple previous is banana The results: Item is now banana next is orange previous is None Print "Item is now", item, "next is", nxt, "previous is", previous Then use it in a loop, and you'll have previous and next items in it: mylist = įor previous, item, nxt in previous_and_next(mylist): Prevs, items, nexts = tee(some_iterable, 3) from itertools import tee, islice, chain, izip Not exactly what your code does, but it is worth taking a look, because it can probably solve your problem. ![]() using the itertools module, splits and slices the iterable, and generates tuples with the previous and next elements together. The title of your question says " Previous and next values inside a loop", but if you run most answers here inside a loop, you'll end up iterating over the entire list again on each element to find it. In my experience a lot of times that isn't possible.Īlso, they don't deal with the fact that you can have repeated elements in the list. Solutions until now only deal with lists, and most are copying the list.
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