Python slice first and last element in list

Question

Is there a way to slice only the first and last item in a list?

For example; If this is my list:

>>> some_list
[\'1\', \'B\', \'3\', \'D\',          


        

Answer 1

One way:

some_list[::len(some_list)-1]

A better way (Doesn't use slicing, but is easier to read):

[some_list[0], some_list[-1]]

Answer 2

You can do it like this:

some_list[0::len(some_list)-1]

Answer 3

These are all interesting but what if you have a version number and you don't know the size of any one segment in string from and you want to drop the last segment. Something like 20.0.1.300 and I want to end up with 20.0.1 without the 300 on the end. I have this so far:

str('20.0.1.300'.split('.')[:3])

which returns in list form as:

['20', '0', '1']

How do I get it back to into a single string separated by periods

20.0.1

Answer 4

Fun new approach to "one-lining" the case of an anonymously split thing such that you don't split it twice, but do all the work in one line is using the walrus operator, :=, to perform assignment as an expression, allowing both:

first, last = (split_str := a.split("-"))[0], split_str[-1]

and:

first, last = (split_str := a.split("-"))[::len(split_str)-1]

Mind you, in both cases it's essentially exactly equivalent to doing on one line:

split_str = a.split("-")

then following up with one of:

first, last = split_str[0], split_str[-1]
first, last = split_str[::len(split_str)-1]

including the fact that split_str persists beyond the line it was used and accessed on. It's just technically meeting the requirements of one-lining, while being fairly ugly. I'd never recommend it over unpacking or itemgetter solutions, even if one-lining was mandatory (ruling out the non-walrus versions that explicitly index or slice a named variable and must refer to said named variable twice).

Answer 5

Another python3 solution uses tuple unpacking with the "*" character:

first, *_, last = range(1, 10)

Answer 6

Utilize the packing/unpacking operator to pack the middle of the list into a single variable:

>>> l = ['1', 'B', '3', 'D', '5', 'F']
>>> first, *middle, last = l
>>> first
'1'
>>> middle
['B', '3', 'D', '5']
>>> last
'F'
>>> 

Or, if you want to discard the middle:

>>> l = ['1', 'B', '3', 'D', '5', 'F']
>>> first, *_, last = l
>>> first
'1'
>>> last
'F'
>>>