Add 1 to a number while keeping sign in python

Question

How can I go from:

lst = [-2, -4, 5, 7]

to:

lstmod = [-3, -5, 6, 8]

I want to add 1 (or a given x value) to each number's magnitude, while keeping the sign. I also want the result to be a list with the same order.

Hey there Elena! Can you show us what code you've tried, and what output you're getting? — Nathaniel Ford, Jun 23 '22 at 16:14
Please provide enough code so others can better understand or reproduce the problem. — Community, Jun 23 '22 at 16:15
If the number is less than zero, subtract one, otherwise add one. What is the difficulty? — John Gordon, Jun 23 '22 at 16:17

score 2 · Answer 1 · answered Jun 23 '22 at 16:16

2

You can use list comprehension as follows:

lst = [-2, -4, 5, 7]
lst = [(i-1) if i < 0 else (i+1) if i > 0 else 0 for i in lst]

print(lst)

Output:

[-3, -5, 6, 8]

answered Jun 23 '22 at 16:16

Cardstdani

score 0 · Answer 2 · answered Jun 23 '22 at 16:20

0

IIUC, you can use:

lst = [-2, -4, 5, 7]
lstmod = [num+1 if num > 0 else num-1 for num in lst]

prints:

[-3, -5, 6, 8]

answered Jun 23 '22 at 16:20

sophocles

3

Even shorter `[num + (num > 0 or -1) for num in lst]` – Olvin Roght Jun 23 '22 at 16:23
indeed. But maybe syntactically is simpler to use the one above. – sophocles Jun 23 '22 at 16:25
@OlvinRoght shorter: yes. easier to understand: no. – Sören Jun 23 '22 at 16:30
@Sören, that's why it's a comment not an answer ;) There're plenty of implicit implementations, here is another one which covers zeros `[num + (num > 0) - (num < 0) for num in lst]` – Olvin Roght Jun 23 '22 at 16:32

score 0 · Answer 3 · answered Jun 23 '22 at 16:27

0

Slight variation on @Cardstdani's and @sophocles' answer:

lst = [-2, -4, 5, 7]
lstmod = [ num + sign(num) for num in lst ]

where sign is any of the functions from this question.

answered Jun 23 '22 at 16:27

Sören

3 Answers3