🔒 list(range(5))[-5:0] should NOT be empty | Python | Page 1

humble kayak Mar 17, 2026, 7:10 PM

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print(list(range(5))[-5:-1])
[0,1,2,3]

but

print(list(range(5))[-5:0])
[] # unexpected, it should be [0,1,2,3,4]

lime flameBOT Mar 17, 2026, 7:10 PM

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humble kayak ```py print(list(range(5))[-5:-1]) [0,1,2,3] ``` but ```py print(list(range(5)...

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@humble kayak

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sterile pilot Mar 17, 2026, 7:23 PM

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humble kayak ```py print(list(range(5))[-5:-1]) [0,1,2,3] ``` but ```py print(list(range(5)...

I don't think it's unexpected. An index of -5 would indicate the first element in the converted list, right? The 0 to the right of the colon would indicate the end index. In this case, because of the list length, -5 points to the same index as 0. So print(list(range(5))[-5:0]) would be the same as saying print(list(range(5))[-5:-5]) or print(list(range(5))[0:0]), and all of these end up printing []

humble kayak Mar 17, 2026, 7:39 PM

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Zero to the right of the colon would indicate that the end index is -1 rather than 0.

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Because A[i:j] takes all elements from A[i] to A[j-1].

vast wasp Mar 17, 2026, 7:50 PM

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0 is the first index

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so if that's the end index, no elements are included

rocky folio Mar 17, 2026, 7:50 PM

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so would it be [0:5]?

humble kayak Mar 17, 2026, 7:50 PM

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[0,1,2,3,4]

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A[0:5] and A[-5:0] should be [0,1,2,3,4].
Because A[-5:0] is the same as subtracting 5 from both index in A[0:5] (I think).

sterile pilot Mar 17, 2026, 7:58 PM

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humble kayak `A[0:5]` and `A[-5:0]` should be `[0,1,2,3,4]`. Because `A[-5:0]` is the same ...

Like I mentioned previously, the indices of -5 and 0 select the same element when slicing a list of length 5. So since the length of the slice is zero when saying A[-5:0] it will result in an empty list.

humble kayak Mar 17, 2026, 8:02 PM

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print(list(range(5))[-3:0]) also produces []

sterile pilot Mar 17, 2026, 8:05 PM

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humble kayak `print(list(range(5))[-3:0])` also produces `[]`

So do any of the following:

print(list(range(5))[-4:0])
print(list(range(5))[-2:0])
print(list(range(5))[-1:0])

I would guess it's because you're trying to slice backwards. In other words the start index of the slice shouldn't be past the end index or it would just result in an empty slice.

humble kayak Mar 17, 2026, 8:08 PM

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Slicing backward is allowed in python.

hoary star Mar 17, 2026, 8:08 PM

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Yes, but you must specify it.

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!e print([0,1,2,3,4][-3:0:-1])

lime flameBOT Mar 17, 2026, 8:08 PM

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hoary star !e `print([0,1,2,3,4][-3:0:-1])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[2, 1]

sterile pilot Mar 17, 2026, 8:12 PM

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Correction to what I said: it's because you're trying to slice backwards when the default is forwards if you leave out that third index

humble kayak Mar 17, 2026, 8:16 PM

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It is also empty print(list(range(5))[-4:-1:-1]) ( Thank you. i would revisit this tomorrow, it is 3:20 AM now, goto sleep;) 🙂

sterile pilot Mar 17, 2026, 8:24 PM

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humble kayak It is also empty `print(list(range(5))[-4:-1:-1])` ( Thank you. i would revisit ...

This is because you're trying to do the opposite: slice forwards when the last index indicates you want to slice backwards.

west holly Mar 17, 2026, 8:35 PM

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humble kayak `A[0:5]` and `A[-5:0]` should be `[0,1,2,3,4]`. Because `A[-5:0]` is the same ...

No, the negative indexing is figured out separately for each one.

celest dragon Mar 17, 2026, 8:41 PM

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No it should be empty

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ind -5 same as ind -1 and index 4

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you're essentially doing arr[-1:-1]

dawn current Mar 17, 2026, 9:33 PM

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!e print(list(range(5))[4:-1:-1])

lime flameBOT Mar 17, 2026, 9:33 PM

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dawn current !e `print(list(range(5))[4:-1:-1])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[]

dawn current Mar 17, 2026, 9:34 PM

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Man wtf

dawn current Mar 17, 2026, 9:56 PM

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!e print(list(range(5))[0:5:-1])

lime flameBOT Mar 17, 2026, 9:56 PM

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dawn current !e `print(list(range(5))[0:5:-1])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[]

dawn current Mar 17, 2026, 9:56 PM

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Ok

exotic forge Mar 17, 2026, 9:56 PM

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!e print(list(range(5))[0:4:-1])

lime flameBOT Mar 17, 2026, 9:56 PM

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exotic forge !e print(list(range(5))[0:4:-1])

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[]

dawn current Mar 17, 2026, 9:57 PM

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!e print(list(range(5))[::-1])

lime flameBOT Mar 17, 2026, 9:57 PM

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dawn current !e `print(list(range(5))[::-1])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[4, 3, 2, 1, 0]

dawn current Mar 17, 2026, 9:57 PM

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Ok so that works

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!e print(list(range(5))[:-1:-1])

lime flameBOT Mar 17, 2026, 9:57 PM

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dawn current !e `print(list(range(5))[:-1:-1])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[]

dawn current Mar 17, 2026, 9:57 PM

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Now why doesn't that work

exotic forge Mar 17, 2026, 9:58 PM

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!e print(list(range(5))[4:0:-1])

lime flameBOT Mar 17, 2026, 9:58 PM

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exotic forge !e `print(list(range(5))[4:0:-1])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[4, 3, 2, 1]

exotic forge Mar 17, 2026, 9:58 PM

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here

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It's just reversed

dawn current Mar 17, 2026, 9:59 PM

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dawn current !e `print(list(range(5))[4:-1:-1])`

This should have worked then

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OHHHHH

exotic forge Mar 17, 2026, 9:59 PM

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!e print(list(range(5))[-1:-5:-1])

lime flameBOT Mar 17, 2026, 9:59 PM

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exotic forge !e print(list(range(5))[-1:-5:-1])

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[4, 3, 2, 1]

dawn current Mar 17, 2026, 9:59 PM

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-1 is last I'm so dumb

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so you have to use None or empty

exotic forge Mar 17, 2026, 10:00 PM

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Where?

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In slicing syntax?

dawn current Mar 17, 2026, 10:00 PM

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In stop spot

exotic forge Mar 17, 2026, 10:00 PM

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Just empty

dawn current Mar 17, 2026, 10:00 PM

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!e print(list(range(5))[4:None:-1])

lime flameBOT Mar 17, 2026, 10:00 PM

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dawn current !e `print(list(range(5))[4:None:-1])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[4, 3, 2, 1, 0]

exotic forge Mar 17, 2026, 10:00 PM

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oh

dawn current Mar 17, 2026, 10:00 PM

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You can use None as well

exotic forge Mar 17, 2026, 10:00 PM

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Seems because it works like a slice function

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!docs slice

lime flameBOT Mar 17, 2026, 10:01 PM

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slice


class slice(stop, /)``````py

class slice(start, stop, step=None, /)```
Return a [slice](https://docs.python.org/3/glossary.html#term-slice) object representing the set of indices specified by `range(start, stop, step)`. The *start* and *step* arguments default to `None`.

Slice objects are also generated when [slicing syntax](https://docs.python.org/3/reference/expressions.html#slicings) is used. For example: `a[start:stop:step]` or `a[start:stop, i]`.

See [`itertools.islice()`](https://docs.python.org/3/library/itertools.html#itertools.islice) for an alternate version that returns an [iterator](https://docs.python.org/3/glossary.html#term-iterator).

dawn current Mar 17, 2026, 10:01 PM

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it makes a slice object yes. Slice is a class

exotic forge Mar 17, 2026, 10:01 PM

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!e print(list(range(5))[slice(0, 4)])

lime flameBOT Mar 17, 2026, 10:01 PM

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exotic forge !e `print(list(range(5))[slice(0, 4)])`

:white_check_mark: Your 3.14 eval job has completed with return code 0.

[0, 1, 2, 3]

exotic forge Mar 17, 2026, 10:01 PM

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cool

lime flameBOT Mar 17, 2026, 11:01 PM

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#🔒 list(range(5))[-5:0] should NOT be empty