Get only the last element of an iterator in the most Pythonic way

Question

How do I get the last element of an iterator? I'm aware that I have to exhaust the iterator and return the last value it produced, so the plain approach would be:

def last(it):
    for value in it:
        pass
    return value

(You might want to catch the NameError and raise something else for empty input, but you get the idea.)

Is there a simpler solution I didn't think of, e. g. using itertools.islice() (it doesn't seem to accept negative indexes, though) or something similar?

you can refer [here](https://stackoverflow.com/questions/2138873/cleanest-way-to-get-last-item-from-python-iterator) — Shijith, Jun 04 '19 at 12:02

yatu · Answer 1 · 2019-06-04T12:05:26.307

5

A simpler solution could be to use Extended Iterable Unpacking:

*_, last = it

Example:

it = range(10)
*_, last = it
print(last)
# 9

edited Jun 04 '19 at 12:05

answered Jun 04 '19 at 11:59

yatu

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are you sure `range()` returns an iterator and not a list? – Gsk Jun 04 '19 at 12:03
@Gsk `isinstance(range(10), list)` – yatu Jun 04 '19 at 12:03
1

Unfortunately it comes close to `list(it)[-1]` which keeps all elements in memory at once as well (your solution stores them briefly in `_`). – Alfe Jun 04 '19 at 12:07
@yatu sorry, wrong wording of the question: [`range()` returns an iterable, not an iterator](https://stackoverflow.com/questions/21803830/why-is-the-range-object-not-an-iterator). I'm just curious, I find your answer interesting – Gsk Jun 04 '19 at 12:10

score 2 · Answer 2 · answered Jun 04 '19 at 11:58

2

Maybe you can use

list(it)[-1]

where it is the iterator.

You convert it into a list and get the last element.

answered Jun 04 '19 at 11:58

J...S

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This stores all elements in memory briefly, just to get the last one eventually. – Alfe Jun 04 '19 at 12:07

score 1 · Answer 3 · answered Jun 04 '19 at 12:04

1

This is not a pythonic way but just some other solution. If you are ok to use toolz. Then you can do the following.

from toolz import last

last(it)

answered Jun 04 '19 at 12:04

Praveenkumar

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score 1 · Answer 4 · answered Jun 04 '19 at 12:09

The following is about 26% faster than

def last(it):
    for value in it:
        pass
    return value

as it does the iteration outside of the interpreter:

import collections
def last(iterator):
    return collections.deque(iterator, maxlen=1).pop()

This raises IndexError if the deque is empty otherwise it returns the last value.

The idea for this comes from the consume example in the itertools module.

Get only the last element of an iterator in the most Pythonic way

4 Answers4