How to get last items of a list in Python

Question

I need the last 9 numbers of a list and I m sure there is a way to do it with slicing  but I can t seem to get it   I can get the first 9 like this   num list 0 9

User · Answer

The last 9 elements can be read from left to right using numlist -9    or from right to left using numlist  -10 -1   as you want    gt  gt  gt  a range 17   gt  gt  gt  print a  0  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16   gt  gt  gt  print a -9    8  9  10  11  12  13  14  15  16   gt  gt  gt  print a  -10 -1   16  15  14  13  12  11  10  9  8

User · Answer

Here are several options for getting the  tail  items of an iterable   Given  n   9 iterable    1  2  3  4  5  6  7  8  9  10    Desired Output   2  3  4  5  6  7  8  9  10    Code  We get the latter output using any of the following options   from collections import deque import itertools  import more itertools     A  Slicing iterable -n       B  Implement an itertools recipe def tail n  iterable          Return an iterator over the last  n  items of  iterable             gt  gt  gt  t   tail 3   ABCDEFG            gt  gt  gt  list t            E    F    G                return iter deque iterable  maxlen n   list tail n  iterable       C  Use an implemented recipe  via more itertools list more itertools tail n  iterable       D  islice  via itertools list itertools islice iterable  len iterable -n  None       E  Negative islice  via more itertools list more itertools islice extended iterable  -n  None       Details   A  Traditional Python slicing is inherent to the language   This option works with sequences such as strings  lists and tuples   However  this kind of slicing does not work on iterators  e g  iter iterable    B  An itertools recipe   It is generalized to work on any iterable and resolves the iterator issue in the last solution   This recipe must be implemented manually as it is not officially included in the itertools module  C  Many recipes  including the latter tool  B   have been conveniently implemented in third party packages   Installing and importing these these libraries obviates manual implementation   One of these libraries is called more itertools  install via  gt  pip install more-itertools   see more itertools tail  D  A member of the itertools library   Note  itertools islice does not support negative slicing    E  Another tool is implemented in more itertools that generalizes itertools islice to support negative slicing  see more itertools islice extended    Which one do I use   It depends   In most cases  slicing  option A  as mentioned in other answers  is most simple option as it built into the language and supports most iterable types   For more general iterators  use any of the remaining options   Note  options C and E require installing a third-party library  which some users may find useful

User · Answer

Slicing  Python slicing is an incredibly fast operation  and it s a handy way to quickly access parts of your data    Slice notation to get the last nine elements from a list  or any other sequence that supports it  like a string  would look like this   num list -9     When I see this  I read the part in the brackets as  9th from the end  to the end    Actually  I abbreviate it mentally as  -9  on    Explanation   The full notation is   sequence start stop step    But the colon is what tells Python you re giving it a slice and not a regular index  That s why the idiomatic way of copying lists in Python 2 is   list copy   sequence      And clearing them is with   del my list       Lists get list copy and list clear in Python 3     Give your slices a descriptive name   You may find it useful to separate forming the slice from passing it to the list   getitem   method  that s what the square brackets do   Even if you re not new to it  it keeps your code more readable so that others that may have to read your code can more readily understand what you re doing   However  you can t just assign some integers separated by colons to a variable  You need to use the slice object   last nine slice   slice -9  None    The second argument  None  is required  so that the first argument is interpreted as the start argument otherwise it would be the stop argument    You can then pass the slice object to your sequence    gt  gt  gt  list range 100   last nine slice   91  92  93  94  95  96  97  98  99    islice  islice from the itertools module is another possibly performant way to get this  islice doesn t take negative arguments  so ideally your iterable has a   reversed   special method - which list does have - so you must first pass your list  or iterable with   reversed    to reversed    gt  gt  gt  from itertools import islice  gt  gt  gt  islice reversed range 100    0  9   lt itertools islice object at 0xffeb87fc gt    islice allows for lazy evaluation of the data pipeline  so to materialize the data  pass it to a constructor  like list     gt  gt  gt  list islice reversed range 100    0  9    99  98  97  96  95  94  93  92  91

User · Answer

a negative index will count from the end of the list  so   num list -9

User · Answer

You can use negative integers with the slicing operator for that  Here s an example using the python CLI interpreter    gt  gt  gt  a    1  2  3  4  5  6  7  8  9  10  11  12   gt  gt  gt  a  1  2  3  4  5  6  7  8  9  10  11  12   gt  gt  gt  a -9    4  5  6  7  8  9  10  11  12    the important line is a -9

[python] How to get last items of a list in Python?

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