Python, assign the last three elements of a list to individual variables

Question

I'd like to assign the last 3 items of a list to individual variables. What I did was:

 l = ["1", "2", "3", "4", "5"]
 a, b ,c = l[-1], l[-2], l[-3]

So a = "5", b = "4" c = "3".

It works, but I'm 99% sure there's a much better way to do this. I tried various for loops, but couldn't make it work at all. So what I' m looking for is essentially just a better version of this, getting X amount of items from the end of a list.

I'm very new to programming, and my Google-Fu failed me so I decided to ask here.

EDIT:

Thanks for the answers, though I was naive enough to think my question was the solution I needed. 100% my fault for not being exact, like the page before asking a question tells you. The answers so far sure did answer what I asked, so thanks a lot for helping me, I already learned something.

What I actually wanted to do is following:

I have a big list (in reality, not in this example), I would like to have the last three items from it and add them after a string. I want to have each list item as an individual variable (maybe not the right way to say it, but as something to add to the end of a string) to add to an existing string, as such:

a = ["1", "2", "3", "4", "5"]
for i in a:
    print("something"+a[-i])

What I wanted to do is:

something + 5
something + 4
something + 3

That didn't work, unfortunately. Iterating the list from the end, but only to a certain point (in this case 3rd item from the end) is something I'd like to learn.

Maybe the question I already asked could be used to do this, obut I just can't make it work. Apologies for my first question anyway, it was terrible by all means.

Possible duplicate of http://stackoverflow.com/questions/646644/how-to-get-last-items-of-a-list-in-python — Forge, Feb 19 '16 at 21:57
@HughBothwell Sorry...just saw that you answered this as a comment after I posted. — idjaw, Feb 19 '16 at 21:58
@idjaw: no problem, I just thought it was too trivial to merit a full answer. — Hugh Bothwell, Feb 19 '16 at 21:58
@HughBothwell :) and I thought it was too tempting to NOT answer. :P — idjaw, Feb 19 '16 at 21:58
@Forge the linked post doesn't demonstrate the destructuring assignment so only half-answers this question. — Ben, Feb 19 '16 at 22:00

Garrett R · Answer 1 · 2016-02-19T22:08:40.263

3

Slice starting at 3 elements from the end of the list.

 l = ["1", "2", "3", "4", "5"]
 a, b ,c = l[-3:] #a,b,c = 3,4,5
 a, b ,c = reversed(l[-3:]) #a,b,c = 5,4,3

edited Feb 19 '16 at 22:08

answered Feb 19 '16 at 22:00

Garrett R

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Well, you have to reverse something somewhere. OP wanted `a` to be `"5"`. – John Y Feb 19 '16 at 22:06

Padraic Cunningham · Accepted Answer · 2016-02-19T22:35:59.680

If you are using python3 you can use extended iterable unpacking:

In [14]: l = ["1", "2", "3", "4", "5"]

In [15]: *_, c, b, a = l

In [16]: a,b,c
Out[16]: ('5', '4', '3')

Based on your edit, if you want to get n items from the list starting at the end and perform some function on them, you can use reversed to start at the end and islice n items from the list:

In [51]: from itertools import islice

In [52]: l = ["1", "2", "3", "4", "5"]

In [53]: c, b, a =  map("something{}".format ,  islice(reversed(l), 3))

In [54]: a,b,c
Out[54]: ('something3', 'something4', 'something5')

Or using your example for loop:

In [55]: for ele in islice(reversed(l), 3):
   ....:     print("Something{}".format(ele))
   ....:     
Something5
Something4
Something3

This is certainly new to me, but seems to be what I'm looking for. Thanks! — PeKo, Feb 20 '16 at 10:06

score 0 · Answer 3 · answered Feb 19 '16 at 22:01

0

Use negative Indexing with negative step, to get the last three elements reversed:

l = ["1", "2", "3", "4", "5"]
a,b,c = l[:-4:-1]
# a = "5", b = "4", c = "3"

answered Feb 19 '16 at 22:01

Daniel

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Python, assign the last three elements of a list to individual variables

3 Answers3